Calculus Examples

Find the Absolute Max and Min over the Interval
f(x)=x4-4x2 , [-3,4]
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.
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Step 1.1.1.1.1
By the Sum Rule, the derivative of x4-4x2 with respect to x is ddx[x4]+ddx[-4x2].
ddx[x4]+ddx[-4x2]
Step 1.1.1.1.2
Differentiate using the Power Rule which states that ddx[xn] is nxn-1 where n=4.
4x3+ddx[-4x2]
4x3+ddx[-4x2]
Step 1.1.1.2
Evaluate ddx[-4x2].
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Step 1.1.1.2.1
Since -4 is constant with respect to x, the derivative of -4x2 with respect to x is -4ddx[x2].
4x3-4ddx[x2]
Step 1.1.1.2.2
Differentiate using the Power Rule which states that ddx[xn] is nxn-1 where n=2.
4x3-4(2x)
Step 1.1.1.2.3
Multiply 2 by -4.
f(x)=4x3-8x
f(x)=4x3-8x
f(x)=4x3-8x
Step 1.1.2
The first derivative of f(x) with respect to x is 4x3-8x.
4x3-8x
4x3-8x
Step 1.2
Set the first derivative equal to 0 then solve the equation 4x3-8x=0.
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Step 1.2.1
Set the first derivative equal to 0.
4x3-8x=0
Step 1.2.2
Factor 4x out of 4x3-8x.
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Step 1.2.2.1
Factor 4x out of 4x3.
4x(x2)-8x=0
Step 1.2.2.2
Factor 4x out of -8x.
4x(x2)+4x(-2)=0
Step 1.2.2.3
Factor 4x out of 4x(x2)+4x(-2).
4x(x2-2)=0
4x(x2-2)=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.
x=0
x2-2=0
Step 1.2.4
Set x equal to 0.
x=0
Step 1.2.5
Set x2-2 equal to 0 and solve for x.
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Step 1.2.5.1
Set x2-2 equal to 0.
x2-2=0
Step 1.2.5.2
Solve x2-2=0 for x.
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Step 1.2.5.2.1
Add 2 to both sides of the equation.
x2=2
Step 1.2.5.2.2
Take the specified root of both sides of the equation to eliminate the exponent on the left side.
x=±2
Step 1.2.5.2.3
The complete solution is the result of both the positive and negative portions of the solution.
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Step 1.2.5.2.3.1
First, use the positive value of the ± to find the first solution.
x=2
Step 1.2.5.2.3.2
Next, use the negative value of the ± to find the second solution.
x=-2
Step 1.2.5.2.3.3
The complete solution is the result of both the positive and negative portions of the solution.
x=2,-2
x=2,-2
x=2,-2
x=2,-2
Step 1.2.6
The final solution is all the values that make 4x(x2-2)=0 true.
x=0,2,-2
x=0,2,-2
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 x4-4x2 at each x value where the derivative is 0 or undefined.
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Step 1.4.1
Evaluate at x=0.
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Step 1.4.1.1
Substitute 0 for x.
(0)4-4(0)2
Step 1.4.1.2
Simplify.
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Step 1.4.1.2.1
Simplify each term.
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Step 1.4.1.2.1.1
Raising 0 to any positive power yields 0.
0-4(0)2
Step 1.4.1.2.1.2
Raising 0 to any positive power yields 0.
0-40
Step 1.4.1.2.1.3
Multiply -4 by 0.
0+0
0+0
Step 1.4.1.2.2
Add 0 and 0.
0
0
0
Step 1.4.2
Evaluate at x=2.
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Step 1.4.2.1
Substitute 2 for x.
(2)4-4(2)2
Step 1.4.2.2
Simplify.
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Step 1.4.2.2.1
Simplify each term.
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Step 1.4.2.2.1.1
Rewrite 24 as 22.
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Step 1.4.2.2.1.1.1
Use axn=axn to rewrite 2 as 212.
(212)4-4(2)2
Step 1.4.2.2.1.1.2
Apply the power rule and multiply exponents, (am)n=amn.
2124-4(2)2
Step 1.4.2.2.1.1.3
Combine 12 and 4.
242-4(2)2
Step 1.4.2.2.1.1.4
Cancel the common factor of 4 and 2.
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Step 1.4.2.2.1.1.4.1
Factor 2 out of 4.
2222-4(2)2
Step 1.4.2.2.1.1.4.2
Cancel the common factors.
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Step 1.4.2.2.1.1.4.2.1
Factor 2 out of 2.
2222(1)-4(2)2
Step 1.4.2.2.1.1.4.2.2
Cancel the common factor.
22221-4(2)2
Step 1.4.2.2.1.1.4.2.3
Rewrite the expression.
221-4(2)2
Step 1.4.2.2.1.1.4.2.4
Divide 2 by 1.
22-4(2)2
22-4(2)2
22-4(2)2
22-4(2)2
Step 1.4.2.2.1.2
Raise 2 to the power of 2.
4-4(2)2
Step 1.4.2.2.1.3
Rewrite 22 as 2.
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Step 1.4.2.2.1.3.1
Use axn=axn to rewrite 2 as 212.
4-4(212)2
Step 1.4.2.2.1.3.2
Apply the power rule and multiply exponents, (am)n=amn.
4-42122
Step 1.4.2.2.1.3.3
Combine 12 and 2.
4-4222
Step 1.4.2.2.1.3.4
Cancel the common factor of 2.
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Step 1.4.2.2.1.3.4.1
Cancel the common factor.
4-4222
Step 1.4.2.2.1.3.4.2
Rewrite the expression.
4-421
4-421
Step 1.4.2.2.1.3.5
Evaluate the exponent.
4-42
4-42
Step 1.4.2.2.1.4
Multiply -4 by 2.
4-8
4-8
Step 1.4.2.2.2
Subtract 8 from 4.
-4
-4
-4
Step 1.4.3
Evaluate at x=-2.
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Step 1.4.3.1
Substitute -2 for x.
(-2)4-4(-2)2
Step 1.4.3.2
Simplify.
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Step 1.4.3.2.1
Simplify each term.
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Step 1.4.3.2.1.1
Apply the product rule to -2.
(-1)424-4(-2)2
Step 1.4.3.2.1.2
Raise -1 to the power of 4.
124-4(-2)2
Step 1.4.3.2.1.3
Multiply 24 by 1.
24-4(-2)2
Step 1.4.3.2.1.4
Rewrite 24 as 22.
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Step 1.4.3.2.1.4.1
Use axn=axn to rewrite 2 as 212.
(212)4-4(-2)2
Step 1.4.3.2.1.4.2
Apply the power rule and multiply exponents, (am)n=amn.
2124-4(-2)2
Step 1.4.3.2.1.4.3
Combine 12 and 4.
242-4(-2)2
Step 1.4.3.2.1.4.4
Cancel the common factor of 4 and 2.
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Step 1.4.3.2.1.4.4.1
Factor 2 out of 4.
2222-4(-2)2
Step 1.4.3.2.1.4.4.2
Cancel the common factors.
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Step 1.4.3.2.1.4.4.2.1
Factor 2 out of 2.
2222(1)-4(-2)2
Step 1.4.3.2.1.4.4.2.2
Cancel the common factor.
22221-4(-2)2
Step 1.4.3.2.1.4.4.2.3
Rewrite the expression.
221-4(-2)2
Step 1.4.3.2.1.4.4.2.4
Divide 2 by 1.
22-4(-2)2
22-4(-2)2
22-4(-2)2
22-4(-2)2
Step 1.4.3.2.1.5
Raise 2 to the power of 2.
4-4(-2)2
Step 1.4.3.2.1.6
Apply the product rule to -2.
4-4((-1)222)
Step 1.4.3.2.1.7
Raise -1 to the power of 2.
4-4(122)
Step 1.4.3.2.1.8
Multiply 22 by 1.
4-422
Step 1.4.3.2.1.9
Rewrite 22 as 2.
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Step 1.4.3.2.1.9.1
Use axn=axn to rewrite 2 as 212.
4-4(212)2
Step 1.4.3.2.1.9.2
Apply the power rule and multiply exponents, (am)n=amn.
4-42122
Step 1.4.3.2.1.9.3
Combine 12 and 2.
4-4222
Step 1.4.3.2.1.9.4
Cancel the common factor of 2.
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Step 1.4.3.2.1.9.4.1
Cancel the common factor.
4-4222
Step 1.4.3.2.1.9.4.2
Rewrite the expression.
4-421
4-421
Step 1.4.3.2.1.9.5
Evaluate the exponent.
4-42
4-42
Step 1.4.3.2.1.10
Multiply -4 by 2.
4-8
4-8
Step 1.4.3.2.2
Subtract 8 from 4.
-4
-4
-4
Step 1.4.4
List all of the points.
(0,0),(2,-4),(-2,-4)
(0,0),(2,-4),(-2,-4)
(0,0),(2,-4),(-2,-4)
Step 2
Evaluate at the included endpoints.
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Step 2.1
Evaluate at x=-3.
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Step 2.1.1
Substitute -3 for x.
(-3)4-4(-3)2
Step 2.1.2
Simplify.
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Step 2.1.2.1
Simplify each term.
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Step 2.1.2.1.1
Raise -3 to the power of 4.
81-4(-3)2
Step 2.1.2.1.2
Raise -3 to the power of 2.
81-49
Step 2.1.2.1.3
Multiply -4 by 9.
81-36
81-36
Step 2.1.2.2
Subtract 36 from 81.
45
45
45
Step 2.2
Evaluate at x=4.
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Step 2.2.1
Substitute 4 for x.
(4)4-4(4)2
Step 2.2.2
Simplify.
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Step 2.2.2.1
Simplify each term.
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Step 2.2.2.1.1
Raise 4 to the power of 4.
256-4(4)2
Step 2.2.2.1.2
Raise 4 to the power of 2.
256-416
Step 2.2.2.1.3
Multiply -4 by 16.
256-64
256-64
Step 2.2.2.2
Subtract 64 from 256.
192
192
192
Step 2.3
List all of the points.
(-3,45),(4,192)
(-3,45),(4,192)
Step 3
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: (4,192)
Absolute Minimum: (2,-4),(-2,-4)
Step 4
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