Calculus Examples

Find the Absolute Max and Min over the Interval f(x)=sin(x)cos(x) , [0,2pi]
f(x)=sin(x)cos(x)f(x)=sin(x)cos(x) , [0,2π][0,2π]
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
Differentiate using the Product Rule which states that ddx[f(x)g(x)]ddx[f(x)g(x)] is f(x)ddx[g(x)]+g(x)ddx[f(x)]f(x)ddx[g(x)]+g(x)ddx[f(x)] where f(x)=sin(x)f(x)=sin(x) and g(x)=cos(x)g(x)=cos(x).
sin(x)ddx[cos(x)]+cos(x)ddx[sin(x)]sin(x)ddx[cos(x)]+cos(x)ddx[sin(x)]
Step 1.1.1.2
The derivative of cos(x)cos(x) with respect to xx is -sin(x)sin(x).
sin(x)(-sin(x))+cos(x)ddx[sin(x)]sin(x)(sin(x))+cos(x)ddx[sin(x)]
Step 1.1.1.3
Raise sin(x)sin(x) to the power of 11.
-(sin1(x)sin(x))+cos(x)ddx[sin(x)](sin1(x)sin(x))+cos(x)ddx[sin(x)]
Step 1.1.1.4
Raise sin(x)sin(x) to the power of 11.
-(sin1(x)sin1(x))+cos(x)ddx[sin(x)](sin1(x)sin1(x))+cos(x)ddx[sin(x)]
Step 1.1.1.5
Use the power rule aman=am+naman=am+n to combine exponents.
-sin(x)1+1+cos(x)ddx[sin(x)]sin(x)1+1+cos(x)ddx[sin(x)]
Step 1.1.1.6
Add 11 and 11.
-sin2(x)+cos(x)ddx[sin(x)]sin2(x)+cos(x)ddx[sin(x)]
Step 1.1.1.7
The derivative of sin(x)sin(x) with respect to xx is cos(x)cos(x).
-sin2(x)+cos(x)cos(x)sin2(x)+cos(x)cos(x)
Step 1.1.1.8
Raise cos(x)cos(x) to the power of 11.
-sin2(x)+cos1(x)cos(x)sin2(x)+cos1(x)cos(x)
Step 1.1.1.9
Raise cos(x)cos(x) to the power of 11.
-sin2(x)+cos1(x)cos1(x)sin2(x)+cos1(x)cos1(x)
Step 1.1.1.10
Use the power rule aman=am+naman=am+n to combine exponents.
-sin2(x)+cos(x)1+1sin2(x)+cos(x)1+1
Step 1.1.1.11
Add 11 and 11.
-sin2(x)+cos2(x)sin2(x)+cos2(x)
Step 1.1.1.12
Simplify.
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Step 1.1.1.12.1
Reorder -sin2(x)sin2(x) and cos2(x)cos2(x).
cos2(x)-sin2(x)cos2(x)sin2(x)
Step 1.1.1.12.2
Since both terms are perfect squares, factor using the difference of squares formula, a2-b2=(a+b)(a-b)a2b2=(a+b)(ab) where a=cos(x)a=cos(x) and b=sin(x)b=sin(x).
(cos(x)+sin(x))(cos(x)-sin(x))(cos(x)+sin(x))(cos(x)sin(x))
Step 1.1.1.12.3
Expand (cos(x)+sin(x))(cos(x)-sin(x))(cos(x)+sin(x))(cos(x)sin(x)) using the FOIL Method.
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Step 1.1.1.12.3.1
Apply the distributive property.
cos(x)(cos(x)-sin(x))+sin(x)(cos(x)-sin(x))cos(x)(cos(x)sin(x))+sin(x)(cos(x)sin(x))
Step 1.1.1.12.3.2
Apply the distributive property.
cos(x)cos(x)+cos(x)(-sin(x))+sin(x)(cos(x)-sin(x))cos(x)cos(x)+cos(x)(sin(x))+sin(x)(cos(x)sin(x))
Step 1.1.1.12.3.3
Apply the distributive property.
cos(x)cos(x)+cos(x)(-sin(x))+sin(x)cos(x)+sin(x)(-sin(x))cos(x)cos(x)+cos(x)(sin(x))+sin(x)cos(x)+sin(x)(sin(x))
cos(x)cos(x)+cos(x)(-sin(x))+sin(x)cos(x)+sin(x)(-sin(x))cos(x)cos(x)+cos(x)(sin(x))+sin(x)cos(x)+sin(x)(sin(x))
Step 1.1.1.12.4
Combine the opposite terms in cos(x)cos(x)+cos(x)(-sin(x))+sin(x)cos(x)+sin(x)(-sin(x))cos(x)cos(x)+cos(x)(sin(x))+sin(x)cos(x)+sin(x)(sin(x)).
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Step 1.1.1.12.4.1
Reorder the factors in the terms cos(x)(-sin(x))cos(x)(sin(x)) and sin(x)cos(x)sin(x)cos(x).
cos(x)cos(x)-cos(x)sin(x)+cos(x)sin(x)+sin(x)(-sin(x))cos(x)cos(x)cos(x)sin(x)+cos(x)sin(x)+sin(x)(sin(x))
Step 1.1.1.12.4.2
Add -cos(x)sin(x)cos(x)sin(x) and cos(x)sin(x)cos(x)sin(x).
cos(x)cos(x)+0+sin(x)(-sin(x))cos(x)cos(x)+0+sin(x)(sin(x))
Step 1.1.1.12.4.3
Add cos(x)cos(x)cos(x)cos(x) and 00.
cos(x)cos(x)+sin(x)(-sin(x))cos(x)cos(x)+sin(x)(sin(x))
cos(x)cos(x)+sin(x)(-sin(x))cos(x)cos(x)+sin(x)(sin(x))
Step 1.1.1.12.5
Simplify each term.
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Step 1.1.1.12.5.1
Multiply cos(x)cos(x)cos(x)cos(x).
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Step 1.1.1.12.5.1.1
Raise cos(x)cos(x) to the power of 11.
cos1(x)cos(x)+sin(x)(-sin(x))cos1(x)cos(x)+sin(x)(sin(x))
Step 1.1.1.12.5.1.2
Raise cos(x)cos(x) to the power of 11.
cos1(x)cos1(x)+sin(x)(-sin(x))cos1(x)cos1(x)+sin(x)(sin(x))
Step 1.1.1.12.5.1.3
Use the power rule aman=am+naman=am+n to combine exponents.
cos(x)1+1+sin(x)(-sin(x))cos(x)1+1+sin(x)(sin(x))
Step 1.1.1.12.5.1.4
Add 11 and 11.
cos2(x)+sin(x)(-sin(x))cos2(x)+sin(x)(sin(x))
cos2(x)+sin(x)(-sin(x))cos2(x)+sin(x)(sin(x))
Step 1.1.1.12.5.2
Rewrite using the commutative property of multiplication.
cos2(x)-sin(x)sin(x)cos2(x)sin(x)sin(x)
Step 1.1.1.12.5.3
Multiply -sin(x)sin(x)sin(x)sin(x).
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Step 1.1.1.12.5.3.1
Raise sin(x)sin(x) to the power of 11.
cos2(x)-(sin1(x)sin(x))cos2(x)(sin1(x)sin(x))
Step 1.1.1.12.5.3.2
Raise sin(x)sin(x) to the power of 11.
cos2(x)-(sin1(x)sin1(x))cos2(x)(sin1(x)sin1(x))
Step 1.1.1.12.5.3.3
Use the power rule aman=am+naman=am+n to combine exponents.
cos2(x)-sin(x)1+1cos2(x)sin(x)1+1
Step 1.1.1.12.5.3.4
Add 11 and 11.
cos2(x)-sin2(x)cos2(x)sin2(x)
cos2(x)-sin2(x)cos2(x)sin2(x)
cos2(x)-sin2(x)cos2(x)sin2(x)
Step 1.1.1.12.6
Apply the cosine double-angle identity.
f(x)=cos(2x)f'(x)=cos(2x)
f(x)=cos(2x)f'(x)=cos(2x)
f(x)=cos(2x)f'(x)=cos(2x)
Step 1.1.2
The first derivative of f(x)f(x) with respect to xx is cos(2x)cos(2x).
cos(2x)cos(2x)
cos(2x)cos(2x)
Step 1.2
Set the first derivative equal to 00 then solve the equation cos(2x)=0cos(2x)=0.
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Step 1.2.1
Set the first derivative equal to 00.
cos(2x)=0cos(2x)=0
Step 1.2.2
Take the inverse cosine of both sides of the equation to extract xx from inside the cosine.
2x=arccos(0)2x=arccos(0)
Step 1.2.3
Simplify the right side.
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Step 1.2.3.1
The exact value of arccos(0)arccos(0) is π2π2.
2x=π22x=π2
2x=π22x=π2
Step 1.2.4
Divide each term in 2x=π22x=π2 by 22 and simplify.
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Step 1.2.4.1
Divide each term in 2x=π22x=π2 by 22.
2x2=π222x2=π22
Step 1.2.4.2
Simplify the left side.
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Step 1.2.4.2.1
Cancel the common factor of 22.
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Step 1.2.4.2.1.1
Cancel the common factor.
2x2=π22
Step 1.2.4.2.1.2
Divide x by 1.
x=π22
x=π22
x=π22
Step 1.2.4.3
Simplify the right side.
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Step 1.2.4.3.1
Multiply the numerator by the reciprocal of the denominator.
x=π212
Step 1.2.4.3.2
Multiply π212.
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Step 1.2.4.3.2.1
Multiply π2 by 12.
x=π22
Step 1.2.4.3.2.2
Multiply 2 by 2.
x=π4
x=π4
x=π4
x=π4
Step 1.2.5
The cosine function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from 2π to find the solution in the fourth quadrant.
2x=2π-π2
Step 1.2.6
Solve for x.
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Step 1.2.6.1
Simplify.
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Step 1.2.6.1.1
To write 2π as a fraction with a common denominator, multiply by 22.
2x=2π22-π2
Step 1.2.6.1.2
Combine 2π and 22.
2x=2π22-π2
Step 1.2.6.1.3
Combine the numerators over the common denominator.
2x=2π2-π2
Step 1.2.6.1.4
Multiply 2 by 2.
2x=4π-π2
Step 1.2.6.1.5
Subtract π from 4π.
2x=3π2
2x=3π2
Step 1.2.6.2
Divide each term in 2x=3π2 by 2 and simplify.
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Step 1.2.6.2.1
Divide each term in 2x=3π2 by 2.
2x2=3π22
Step 1.2.6.2.2
Simplify the left side.
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Step 1.2.6.2.2.1
Cancel the common factor of 2.
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Step 1.2.6.2.2.1.1
Cancel the common factor.
2x2=3π22
Step 1.2.6.2.2.1.2
Divide x by 1.
x=3π22
x=3π22
x=3π22
Step 1.2.6.2.3
Simplify the right side.
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Step 1.2.6.2.3.1
Multiply the numerator by the reciprocal of the denominator.
x=3π212
Step 1.2.6.2.3.2
Multiply 3π212.
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Step 1.2.6.2.3.2.1
Multiply 3π2 by 12.
x=3π22
Step 1.2.6.2.3.2.2
Multiply 2 by 2.
x=3π4
x=3π4
x=3π4
x=3π4
x=3π4
Step 1.2.7
Find the period of cos(2x).
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Step 1.2.7.1
The period of the function can be calculated using 2π|b|.
2π|b|
Step 1.2.7.2
Replace b with 2 in the formula for period.
2π|2|
Step 1.2.7.3
The absolute value is the distance between a number and zero. The distance between 0 and 2 is 2.
2π2
Step 1.2.7.4
Cancel the common factor of 2.
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Step 1.2.7.4.1
Cancel the common factor.
2π2
Step 1.2.7.4.2
Divide π by 1.
π
π
π
Step 1.2.8
The period of the cos(2x) function is π so values will repeat every π radians in both directions.
x=π4+πn,3π4+πn, for any integer n
Step 1.2.9
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 sin(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.
sin(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.
22cos(π4)
Step 1.4.1.2.2
The exact value of cos(π4) is 22.
2222
Step 1.4.1.2.3
Multiply 2222.
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Step 1.4.1.2.3.1
Multiply 22 by 22.
2222
Step 1.4.1.2.3.2
Raise 2 to the power of 1.
21222
Step 1.4.1.2.3.3
Raise 2 to the power of 1.
212122
Step 1.4.1.2.3.4
Use the power rule aman=am+n to combine exponents.
21+122
Step 1.4.1.2.3.5
Add 1 and 1.
2222
Step 1.4.1.2.3.6
Multiply 2 by 2.
224
224
Step 1.4.1.2.4
Rewrite 22 as 2.
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Step 1.4.1.2.4.1
Use nax=axn to rewrite 2 as 212.
(212)24
Step 1.4.1.2.4.2
Apply the power rule and multiply exponents, (am)n=amn.
21224
Step 1.4.1.2.4.3
Combine 12 and 2.
2224
Step 1.4.1.2.4.4
Cancel the common factor of 2.
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Step 1.4.1.2.4.4.1
Cancel the common factor.
2224
Step 1.4.1.2.4.4.2
Rewrite the expression.
214
214
Step 1.4.1.2.4.5
Evaluate the exponent.
24
24
Step 1.4.1.2.5
Cancel the common factor of 2 and 4.
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Step 1.4.1.2.5.1
Factor 2 out of 2.
2(1)4
Step 1.4.1.2.5.2
Cancel the common factors.
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Step 1.4.1.2.5.2.1
Factor 2 out of 4.
2122
Step 1.4.1.2.5.2.2
Cancel the common factor.
2122
Step 1.4.1.2.5.2.3
Rewrite the expression.
12
12
12
12
12
Step 1.4.2
Evaluate at x=3π4.
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Step 1.4.2.1
Substitute 3π4 for x.
sin(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.
sin(π4)cos(3π4)
Step 1.4.2.2.2
The exact value of sin(π4) is 22.
22cos(3π4)
Step 1.4.2.2.3
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.
22(-cos(π4))
Step 1.4.2.2.4
The exact value of cos(π4) is 22.
22(-22)
Step 1.4.2.2.5
Multiply 22(-22).
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Step 1.4.2.2.5.1
Multiply 22 by 22.
-2222
Step 1.4.2.2.5.2
Raise 2 to the power of 1.
-21222
Step 1.4.2.2.5.3
Raise 2 to the power of 1.
-212122
Step 1.4.2.2.5.4
Use the power rule aman=am+n to combine exponents.
-21+122
Step 1.4.2.2.5.5
Add 1 and 1.
-2222
Step 1.4.2.2.5.6
Multiply 2 by 2.
-224
-224
Step 1.4.2.2.6
Rewrite 22 as 2.
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Step 1.4.2.2.6.1
Use nax=axn to rewrite 2 as 212.
-(212)24
Step 1.4.2.2.6.2
Apply the power rule and multiply exponents, (am)n=amn.
-21224
Step 1.4.2.2.6.3
Combine 12 and 2.
-2224
Step 1.4.2.2.6.4
Cancel the common factor of 2.
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Step 1.4.2.2.6.4.1
Cancel the common factor.
-2224
Step 1.4.2.2.6.4.2
Rewrite the expression.
-214
-214
Step 1.4.2.2.6.5
Evaluate the exponent.
-24
-24
Step 1.4.2.2.7
Cancel the common factor of 2 and 4.
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Step 1.4.2.2.7.1
Factor 2 out of 2.
-2(1)4
Step 1.4.2.2.7.2
Cancel the common factors.
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Step 1.4.2.2.7.2.1
Factor 2 out of 4.
-2122
Step 1.4.2.2.7.2.2
Cancel the common factor.
-2122
Step 1.4.2.2.7.2.3
Rewrite the expression.
-12
-12
-12
-12
-12
Step 1.4.3
List all of the points.
(π4+πn,12),(3π4+πn,-12), for any integer n
(π4+πn,12),(3π4+πn,-12), for any integer n
(π4+πn,12),(3π4+πn,-12), for any integer n
Step 2
Exclude the points that are not on the interval.
(π4,12),(5π4,12),(3π4,-12),(7π4,-12)
Step 3
Evaluate at the included endpoints.
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Step 3.1
Evaluate at x=0.
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Step 3.1.1
Substitute 0 for x.
sin(0)cos(0)
Step 3.1.2
Simplify.
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Step 3.1.2.1
The exact value of sin(0) is 0.
0cos(0)
Step 3.1.2.2
The exact value of cos(0) is 1.
01
Step 3.1.2.3
Multiply 0 by 1.
0
0
0
Step 3.2
Evaluate at x=2π.
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Step 3.2.1
Substitute 2π for x.
sin(2π)cos(2π)
Step 3.2.2
Simplify.
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Step 3.2.2.1
Subtract full rotations of 2π until the angle is greater than or equal to 0 and less than 2π.
sin(0)cos(2π)
Step 3.2.2.2
The exact value of sin(0) is 0.
0cos(2π)
Step 3.2.2.3
Subtract full rotations of 2π until the angle is greater than or equal to 0 and less than 2π.
0cos(0)
Step 3.2.2.4
The exact value of cos(0) is 1.
01
Step 3.2.2.5
Multiply 0 by 1.
0
0
0
Step 3.3
List all of the points.
(0,0),(2π,0)
(0,0),(2π,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: (π4,12),(5π4,12)
Absolute Minimum: (3π4,-12),(7π4,-12)
Step 5
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