Calculus Examples

Find the Absolute Max and Min over the Interval f(x)=3sin(x)cos(x) , [pi/4,pi]
f(x)=3sin(x)cos(x)f(x)=3sin(x)cos(x) , [π4,π]
Step 1
Find the critical points.
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Step 1.1
Find the first derivative.
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Step 1.1.1
Find the first derivative.
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Step 1.1.1.1
Since 3 is constant with respect to x, the derivative of 3sin(x)cos(x) with respect to x is 3ddx[sin(x)cos(x)].
3ddx[sin(x)cos(x)]
Step 1.1.1.2
Differentiate using the Product Rule which states that ddx[f(x)g(x)] is f(x)ddx[g(x)]+g(x)ddx[f(x)] where f(x)=sin(x) and g(x)=cos(x).
3(sin(x)ddx[cos(x)]+cos(x)ddx[sin(x)])
Step 1.1.1.3
The derivative of cos(x) with respect to x is -sin(x).
3(sin(x)(-sin(x))+cos(x)ddx[sin(x)])
Step 1.1.1.4
Raise sin(x) to the power of 1.
3(-(sin1(x)sin(x))+cos(x)ddx[sin(x)])
Step 1.1.1.5
Raise sin(x) to the power of 1.
3(-(sin1(x)sin1(x))+cos(x)ddx[sin(x)])
Step 1.1.1.6
Use the power rule aman=am+n to combine exponents.
3(-sin(x)1+1+cos(x)ddx[sin(x)])
Step 1.1.1.7
Add 1 and 1.
3(-sin2(x)+cos(x)ddx[sin(x)])
Step 1.1.1.8
The derivative of sin(x) with respect to x is cos(x).
3(-sin2(x)+cos(x)cos(x))
Step 1.1.1.9
Raise cos(x) to the power of 1.
3(-sin2(x)+cos1(x)cos(x))
Step 1.1.1.10
Raise cos(x) to the power of 1.
3(-sin2(x)+cos1(x)cos1(x))
Step 1.1.1.11
Use the power rule aman=am+n to combine exponents.
3(-sin2(x)+cos(x)1+1)
Step 1.1.1.12
Add 1 and 1.
3(-sin2(x)+cos2(x))
Step 1.1.1.13
Simplify.
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Step 1.1.1.13.1
Apply the distributive property.
3(-sin2(x))+3cos2(x)
Step 1.1.1.13.2
Multiply -1 by 3.
f(x)=-3sin2(x)+3cos2(x)
f(x)=-3sin2(x)+3cos2(x)
f(x)=-3sin2(x)+3cos2(x)
Step 1.1.2
The first derivative of f(x) with respect to x is -3sin2(x)+3cos2(x).
-3sin2(x)+3cos2(x)
-3sin2(x)+3cos2(x)
Step 1.2
Set the first derivative equal to 0 then solve the equation -3sin2(x)+3cos2(x)=0.
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Step 1.2.1
Set the first derivative equal to 0.
-3sin2(x)+3cos2(x)=0
Step 1.2.2
Factor -3sin2(x)+3cos2(x).
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Step 1.2.2.1
Factor 3 out of -3sin2(x)+3cos2(x).
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Step 1.2.2.1.1
Factor 3 out of -3sin2(x).
3(-sin2(x))+3cos2(x)=0
Step 1.2.2.1.2
Factor 3 out of 3cos2(x).
3(-sin2(x))+3cos2(x)=0
Step 1.2.2.1.3
Factor 3 out of 3(-sin2(x))+3cos2(x).
3(-sin2(x)+cos2(x))=0
3(-sin2(x)+cos2(x))=0
Step 1.2.2.2
Reorder -sin2(x) and cos2(x).
3(cos2(x)-sin2(x))=0
Step 1.2.2.3
Factor.
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Step 1.2.2.3.1
Since both terms are perfect squares, factor using the difference of squares formula, a2-b2=(a+b)(a-b) where a=cos(x) and b=sin(x).
3((cos(x)+sin(x))(cos(x)-sin(x)))=0
Step 1.2.2.3.2
Remove unnecessary parentheses.
3(cos(x)+sin(x))(cos(x)-sin(x))=0
3(cos(x)+sin(x))(cos(x)-sin(x))=0
3(cos(x)+sin(x))(cos(x)-sin(x))=0
Step 1.2.3
If any individual factor on the left side of the equation is equal to 0, the entire expression will be equal to 0.
cos(x)+sin(x)=0
cos(x)-sin(x)=0
Step 1.2.4
Set cos(x)+sin(x) equal to 0 and solve for x.
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Step 1.2.4.1
Set cos(x)+sin(x) equal to 0.
cos(x)+sin(x)=0
Step 1.2.4.2
Solve cos(x)+sin(x)=0 for x.
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Step 1.2.4.2.1
Divide each term in the equation by cos(x).
cos(x)cos(x)+sin(x)cos(x)=0cos(x)
Step 1.2.4.2.2
Cancel the common factor of cos(x).
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Step 1.2.4.2.2.1
Cancel the common factor.
cos(x)cos(x)+sin(x)cos(x)=0cos(x)
Step 1.2.4.2.2.2
Rewrite the expression.
1+sin(x)cos(x)=0cos(x)
1+sin(x)cos(x)=0cos(x)
Step 1.2.4.2.3
Convert from sin(x)cos(x) to tan(x).
1+tan(x)=0cos(x)
Step 1.2.4.2.4
Separate fractions.
1+tan(x)=011cos(x)
Step 1.2.4.2.5
Convert from 1cos(x) to sec(x).
1+tan(x)=01sec(x)
Step 1.2.4.2.6
Divide 0 by 1.
1+tan(x)=0sec(x)
Step 1.2.4.2.7
Multiply 0 by sec(x).
1+tan(x)=0
Step 1.2.4.2.8
Subtract 1 from both sides of the equation.
tan(x)=-1
Step 1.2.4.2.9
Take the inverse tangent of both sides of the equation to extract x from inside the tangent.
x=arctan(-1)
Step 1.2.4.2.10
Simplify the right side.
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Step 1.2.4.2.10.1
The exact value of arctan(-1) is -π4.
x=-π4
x=-π4
Step 1.2.4.2.11
The tangent function is negative in the second and fourth quadrants. To find the second solution, subtract the reference angle from π to find the solution in the third quadrant.
x=-π4-π
Step 1.2.4.2.12
Simplify the expression to find the second solution.
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Step 1.2.4.2.12.1
Add 2π to -π4-π.
x=-π4-π+2π
Step 1.2.4.2.12.2
The resulting angle of 3π4 is positive and coterminal with -π4-π.
x=3π4
x=3π4
Step 1.2.4.2.13
Find the period of tan(x).
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Step 1.2.4.2.13.1
The period of the function can be calculated using π|b|.
π|b|
Step 1.2.4.2.13.2
Replace b with 1 in the formula for period.
π|1|
Step 1.2.4.2.13.3
The absolute value is the distance between a number and zero. The distance between 0 and 1 is 1.
π1
Step 1.2.4.2.13.4
Divide π by 1.
π
π
Step 1.2.4.2.14
Add π to every negative angle to get positive angles.
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Step 1.2.4.2.14.1
Add π to -π4 to find the positive angle.
-π4+π
Step 1.2.4.2.14.2
To write π as a fraction with a common denominator, multiply by 44.
π44-π4
Step 1.2.4.2.14.3
Combine fractions.
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Step 1.2.4.2.14.3.1
Combine π and 44.
π44-π4
Step 1.2.4.2.14.3.2
Combine the numerators over the common denominator.
π4-π4
π4-π4
Step 1.2.4.2.14.4
Simplify the numerator.
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Step 1.2.4.2.14.4.1
Move 4 to the left of π.
4π-π4
Step 1.2.4.2.14.4.2
Subtract π from 4π.
3π4
3π4
Step 1.2.4.2.14.5
List the new angles.
x=3π4
x=3π4
Step 1.2.4.2.15
The period of the tan(x) function is π so values will repeat every π radians in both directions.
x=3π4+πn,3π4+πn, for any integer n
x=3π4+πn,3π4+πn, for any integer n
x=3π4+πn,3π4+πn, for any integer n
Step 1.2.5
Set cos(x)-sin(x) equal to 0 and solve for x.
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Step 1.2.5.1
Set cos(x)-sin(x) equal to 0.
cos(x)-sin(x)=0
Step 1.2.5.2
Solve cos(x)-sin(x)=0 for x.
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Step 1.2.5.2.1
Divide each term in the equation by cos(x).
cos(x)cos(x)+-sin(x)cos(x)=0cos(x)
Step 1.2.5.2.2
Cancel the common factor of cos(x).
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Step 1.2.5.2.2.1
Cancel the common factor.
cos(x)cos(x)+-sin(x)cos(x)=0cos(x)
Step 1.2.5.2.2.2
Rewrite the expression.
1+-sin(x)cos(x)=0cos(x)
1+-sin(x)cos(x)=0cos(x)
Step 1.2.5.2.3
Separate fractions.
1+-11sin(x)cos(x)=0cos(x)
Step 1.2.5.2.4
Convert from sin(x)cos(x) to tan(x).
1+-11tan(x)=0cos(x)
Step 1.2.5.2.5
Divide -1 by 1.
1-tan(x)=0cos(x)
Step 1.2.5.2.6
Separate fractions.
1-tan(x)=011cos(x)
Step 1.2.5.2.7
Convert from 1cos(x) to sec(x).
1-tan(x)=01sec(x)
Step 1.2.5.2.8
Divide 0 by 1.
1-tan(x)=0sec(x)
Step 1.2.5.2.9
Multiply 0 by sec(x).
1-tan(x)=0
Step 1.2.5.2.10
Subtract 1 from both sides of the equation.
-tan(x)=-1
Step 1.2.5.2.11
Divide each term in -tan(x)=-1 by -1 and simplify.
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Step 1.2.5.2.11.1
Divide each term in -tan(x)=-1 by -1.
-tan(x)-1=-1-1
Step 1.2.5.2.11.2
Simplify the left side.
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Step 1.2.5.2.11.2.1
Dividing two negative values results in a positive value.
tan(x)1=-1-1
Step 1.2.5.2.11.2.2
Divide tan(x) by 1.
tan(x)=-1-1
tan(x)=-1-1
Step 1.2.5.2.11.3
Simplify the right side.
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Step 1.2.5.2.11.3.1
Divide -1 by -1.
tan(x)=1
tan(x)=1
tan(x)=1
Step 1.2.5.2.12
Take the inverse tangent of both sides of the equation to extract x from inside the tangent.
x=arctan(1)
Step 1.2.5.2.13
Simplify the right side.
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Step 1.2.5.2.13.1
The exact value of arctan(1) is π4.
x=π4
x=π4
Step 1.2.5.2.14
The tangent function is positive in the first and third quadrants. To find the second solution, add the reference angle from π to find the solution in the fourth quadrant.
x=π+π4
Step 1.2.5.2.15
Simplify π+π4.
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Step 1.2.5.2.15.1
To write π as a fraction with a common denominator, multiply by 44.
x=π44+π4
Step 1.2.5.2.15.2
Combine fractions.
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Step 1.2.5.2.15.2.1
Combine π and 44.
x=π44+π4
Step 1.2.5.2.15.2.2
Combine the numerators over the common denominator.
x=π4+π4
x=π4+π4
Step 1.2.5.2.15.3
Simplify the numerator.
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Step 1.2.5.2.15.3.1
Move 4 to the left of π.
x=4π+π4
Step 1.2.5.2.15.3.2
Add 4π and π.
x=5π4
x=5π4
x=5π4
Step 1.2.5.2.16
Find the period of tan(x).
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Step 1.2.5.2.16.1
The period of the function can be calculated using π|b|.
π|b|
Step 1.2.5.2.16.2
Replace b with 1 in the formula for period.
π|1|
Step 1.2.5.2.16.3
The absolute value is the distance between a number and zero. The distance between 0 and 1 is 1.
π1
Step 1.2.5.2.16.4
Divide π by 1.
π
π
Step 1.2.5.2.17
The period of the tan(x) function is π so values will repeat every π radians in both directions.
x=π4+πn,5π4+πn, for any integer n
x=π4+πn,5π4+πn, for any integer n
x=π4+πn,5π4+πn, for any integer n
Step 1.2.6
The final solution is all the values that make 3(cos(x)+sin(x))(cos(x)-sin(x))=0 true.
x=3π4+πn,π4+πn,5π4+πn, for any integer n
Step 1.2.7
Consolidate the answers.
x=π4+πn2, for any integer n
x=π4+πn2, for any integer n
Step 1.3
Find the values where the derivative is undefined.
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Step 1.3.1
The domain of the expression is all real numbers except where the expression is undefined. In this case, there is no real number that makes the expression undefined.
Step 1.4
Evaluate 3sin(x)cos(x) at each x value where the derivative is 0 or undefined.
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Step 1.4.1
Evaluate at x=π4.
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Step 1.4.1.1
Substitute π4 for x.
3sin(π4)cos(π4)
Step 1.4.1.2
Simplify.
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Step 1.4.1.2.1
The exact value of sin(π4) is 22.
322cos(π4)
Step 1.4.1.2.2
Combine 3 and 22.
322cos(π4)
Step 1.4.1.2.3
The exact value of cos(π4) is 22.
32222
Step 1.4.1.2.4
Multiply 32222.
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Step 1.4.1.2.4.1
Multiply 322 by 22.
32222
Step 1.4.1.2.4.2
Raise 2 to the power of 1.
3(212)22
Step 1.4.1.2.4.3
Raise 2 to the power of 1.
3(2121)22
Step 1.4.1.2.4.4
Use the power rule aman=am+n to combine exponents.
321+122
Step 1.4.1.2.4.5
Add 1 and 1.
32222
Step 1.4.1.2.4.6
Multiply 2 by 2.
3224
3224
Step 1.4.1.2.5
Rewrite 22 as 2.
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Step 1.4.1.2.5.1
Use nax=axn to rewrite 2 as 212.
3(212)24
Step 1.4.1.2.5.2
Apply the power rule and multiply exponents, (am)n=amn.
321224
Step 1.4.1.2.5.3
Combine 12 and 2.
32224
Step 1.4.1.2.5.4
Cancel the common factor of 2.
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Step 1.4.1.2.5.4.1
Cancel the common factor.
32224
Step 1.4.1.2.5.4.2
Rewrite the expression.
3214
3214
Step 1.4.1.2.5.5
Evaluate the exponent.
324
324
Step 1.4.1.2.6
Multiply 3 by 2.
64
Step 1.4.1.2.7
Cancel the common factor of 6 and 4.
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Step 1.4.1.2.7.1
Factor 2 out of 6.
2(3)4
Step 1.4.1.2.7.2
Cancel the common factors.
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Step 1.4.1.2.7.2.1
Factor 2 out of 4.
2322
Step 1.4.1.2.7.2.2
Cancel the common factor.
2322
Step 1.4.1.2.7.2.3
Rewrite the expression.
32
32
32
32
32
Step 1.4.2
Evaluate at x=3π4.
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Step 1.4.2.1
Substitute 3π4 for x.
3sin(3π4)cos(3π4)
Step 1.4.2.2
Simplify.
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Step 1.4.2.2.1
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.
3sin(π4)cos(3π4)
Step 1.4.2.2.2
The exact value of sin(π4) is 22.
322cos(3π4)
Step 1.4.2.2.3
Combine 3 and 22.
322cos(3π4)
Step 1.4.2.2.4
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.
322(-cos(π4))
Step 1.4.2.2.5
The exact value of cos(π4) is 22.
322(-22)
Step 1.4.2.2.6
Multiply 322(-22).
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Step 1.4.2.2.6.1
Multiply 322 by 22.
-32222
Step 1.4.2.2.6.2
Raise 2 to the power of 1.
-3(212)22
Step 1.4.2.2.6.3
Raise 2 to the power of 1.
-3(2121)22
Step 1.4.2.2.6.4
Use the power rule aman=am+n to combine exponents.
-321+122
Step 1.4.2.2.6.5
Add 1 and 1.
-32222
Step 1.4.2.2.6.6
Multiply 2 by 2.
-3224
-3224
Step 1.4.2.2.7
Rewrite 22 as 2.
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Step 1.4.2.2.7.1
Use nax=axn to rewrite 2 as 212.
-3(212)24
Step 1.4.2.2.7.2
Apply the power rule and multiply exponents, (am)n=amn.
-321224
Step 1.4.2.2.7.3
Combine 12 and 2.
-32224
Step 1.4.2.2.7.4
Cancel the common factor of 2.
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Step 1.4.2.2.7.4.1
Cancel the common factor.
-32224
Step 1.4.2.2.7.4.2
Rewrite the expression.
-3214
-3214
Step 1.4.2.2.7.5
Evaluate the exponent.
-324
-324
Step 1.4.2.2.8
Multiply 3 by 2.
-64
Step 1.4.2.2.9
Cancel the common factor of 6 and 4.
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Step 1.4.2.2.9.1
Factor 2 out of 6.
-2(3)4
Step 1.4.2.2.9.2
Cancel the common factors.
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Step 1.4.2.2.9.2.1
Factor 2 out of 4.
-2322
Step 1.4.2.2.9.2.2
Cancel the common factor.
-2322
Step 1.4.2.2.9.2.3
Rewrite the expression.
-32
-32
-32
-32
-32
Step 1.4.3
List all of the points.
(π4+πn,32),(3π4+πn,-32), for any integer n
(π4+πn,32),(3π4+πn,-32), for any integer n
(π4+πn,32),(3π4+πn,-32), for any integer n
Step 2
Exclude the points that are not on the interval.
(π4,32),(3π4,-32)
Step 3
Evaluate at the included endpoints.
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Step 3.1
Evaluate at x=π4.
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Step 3.1.1
Substitute π4 for x.
3sin(π4)cos(π4)
Step 3.1.2
Simplify.
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Step 3.1.2.1
The exact value of sin(π4) is 22.
322cos(π4)
Step 3.1.2.2
Combine 3 and 22.
322cos(π4)
Step 3.1.2.3
The exact value of cos(π4) is 22.
32222
Step 3.1.2.4
Multiply 32222.
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Step 3.1.2.4.1
Multiply 322 by 22.
32222
Step 3.1.2.4.2
Raise 2 to the power of 1.
3(212)22
Step 3.1.2.4.3
Raise 2 to the power of 1.
3(2121)22
Step 3.1.2.4.4
Use the power rule aman=am+n to combine exponents.
321+122
Step 3.1.2.4.5
Add 1 and 1.
32222
Step 3.1.2.4.6
Multiply 2 by 2.
3224
3224
Step 3.1.2.5
Rewrite 22 as 2.
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Step 3.1.2.5.1
Use nax=axn to rewrite 2 as 212.
3(212)24
Step 3.1.2.5.2
Apply the power rule and multiply exponents, (am)n=amn.
321224
Step 3.1.2.5.3
Combine 12 and 2.
32224
Step 3.1.2.5.4
Cancel the common factor of 2.
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Step 3.1.2.5.4.1
Cancel the common factor.
32224
Step 3.1.2.5.4.2
Rewrite the expression.
3214
3214
Step 3.1.2.5.5
Evaluate the exponent.
324
324
Step 3.1.2.6
Multiply 3 by 2.
64
Step 3.1.2.7
Cancel the common factor of 6 and 4.
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Step 3.1.2.7.1
Factor 2 out of 6.
2(3)4
Step 3.1.2.7.2
Cancel the common factors.
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Step 3.1.2.7.2.1
Factor 2 out of 4.
2322
Step 3.1.2.7.2.2
Cancel the common factor.
2322
Step 3.1.2.7.2.3
Rewrite the expression.
32
32
32
32
32
Step 3.2
Evaluate at x=π.
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Step 3.2.1
Substitute π for x.
3sin(π)cos(π)
Step 3.2.2
Simplify.
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Step 3.2.2.1
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.
3sin(0)cos(π)
Step 3.2.2.2
The exact value of sin(0) is 0.
30cos(π)
Step 3.2.2.3
Multiply 3 by 0.
0cos(π)
Step 3.2.2.4
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.
0(-cos(0))
Step 3.2.2.5
The exact value of cos(0) is 1.
0(-11)
Step 3.2.2.6
Multiply 0(-11).
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Step 3.2.2.6.1
Multiply -1 by 1.
0-1
Step 3.2.2.6.2
Multiply 0 by -1.
0
0
0
0
Step 3.3
List all of the points.
(π4,32),(π,0)
(π4,32),(π,0)
Step 4
Compare the f(x) values found for each value of x in order to determine the absolute maximum and minimum over the given interval. The maximum will occur at the highest f(x) value and the minimum will occur at the lowest f(x) value.
Absolute Maximum: (π4,32)
Absolute Minimum: (3π4,-32)
Step 5
 [x2  12  π  xdx ]