Calculus Examples

Find the Local Maxima and Minima f(x)=e^xcos(x)
Step 1
Find the first derivative of the function.
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Step 1.1
Differentiate using the Product Rule which states that is where and .
Step 1.2
The derivative of with respect to is .
Step 1.3
Differentiate using the Exponential Rule which states that is where =.
Step 1.4
Reorder terms.
Step 2
Find the second derivative of the function.
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Step 2.1
By the Sum Rule, the derivative of with respect to is .
Step 2.2
Evaluate .
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Step 2.2.1
Since is constant with respect to , the derivative of with respect to is .
Step 2.2.2
Differentiate using the Product Rule which states that is where and .
Step 2.2.3
The derivative of with respect to is .
Step 2.2.4
Differentiate using the Exponential Rule which states that is where =.
Step 2.3
Evaluate .
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Step 2.3.1
Differentiate using the Product Rule which states that is where and .
Step 2.3.2
The derivative of with respect to is .
Step 2.3.3
Differentiate using the Exponential Rule which states that is where =.
Step 2.4
Simplify.
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Step 2.4.1
Apply the distributive property.
Step 2.4.2
Combine terms.
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Step 2.4.2.1
Reorder and .
Step 2.4.2.2
Rewrite as .
Step 2.4.2.3
Subtract from .
Step 2.4.2.4
Add and .
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Step 2.4.2.4.1
Reorder and .
Step 2.4.2.4.2
Add and .
Step 2.4.2.5
Add and .
Step 3
To find the local maximum and minimum values of the function, set the derivative equal to and solve.
Step 4
Factor .
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Step 4.1
Factor out of .
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Step 4.1.1
Factor out of .
Step 4.1.2
Factor out of .
Step 4.1.3
Factor out of .
Step 4.2
Rewrite as .
Step 5
If any individual factor on the left side of the equation is equal to , the entire expression will be equal to .
Step 6
Set equal to and solve for .
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Step 6.1
Set equal to .
Step 6.2
Solve for .
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Step 6.2.1
Take the natural logarithm of both sides of the equation to remove the variable from the exponent.
Step 6.2.2
The equation cannot be solved because is undefined.
Undefined
Step 6.2.3
There is no solution for
No solution
No solution
No solution
Step 7
Set equal to and solve for .
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Step 7.1
Set equal to .
Step 7.2
Solve for .
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Step 7.2.1
Divide each term in the equation by .
Step 7.2.2
Separate fractions.
Step 7.2.3
Convert from to .
Step 7.2.4
Divide by .
Step 7.2.5
Cancel the common factor of .
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Step 7.2.5.1
Cancel the common factor.
Step 7.2.5.2
Rewrite the expression.
Step 7.2.6
Separate fractions.
Step 7.2.7
Convert from to .
Step 7.2.8
Divide by .
Step 7.2.9
Multiply by .
Step 7.2.10
Subtract from both sides of the equation.
Step 7.2.11
Divide each term in by and simplify.
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Step 7.2.11.1
Divide each term in by .
Step 7.2.11.2
Simplify the left side.
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Step 7.2.11.2.1
Dividing two negative values results in a positive value.
Step 7.2.11.2.2
Divide by .
Step 7.2.11.3
Simplify the right side.
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Step 7.2.11.3.1
Divide by .
Step 7.2.12
Take the inverse tangent of both sides of the equation to extract from inside the tangent.
Step 7.2.13
Simplify the right side.
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Step 7.2.13.1
The exact value of is .
Step 7.2.14
The tangent function is positive in the first and third quadrants. To find the second solution, add the reference angle from to find the solution in the fourth quadrant.
Step 7.2.15
Simplify .
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Step 7.2.15.1
To write as a fraction with a common denominator, multiply by .
Step 7.2.15.2
Combine fractions.
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Step 7.2.15.2.1
Combine and .
Step 7.2.15.2.2
Combine the numerators over the common denominator.
Step 7.2.15.3
Simplify the numerator.
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Step 7.2.15.3.1
Move to the left of .
Step 7.2.15.3.2
Add and .
Step 7.2.16
The solution to the equation .
Step 8
The final solution is all the values that make true.
Step 9
Evaluate the second derivative at . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.
Step 10
Evaluate the second derivative.
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Step 10.1
The exact value of is .
Step 10.2
Cancel the common factor of .
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Step 10.2.1
Factor out of .
Step 10.2.2
Cancel the common factor.
Step 10.2.3
Rewrite the expression.
Step 11
is a local maximum because the value of the second derivative is negative. This is referred to as the second derivative test.
is a local maximum
Step 12
Find the y-value when .
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Step 12.1
Replace the variable with in the expression.
Step 12.2
Simplify the result.
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Step 12.2.1
The exact value of is .
Step 12.2.2
Combine and .
Step 12.2.3
The final answer is .
Step 13
Evaluate the second derivative at . If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.
Step 14
Evaluate the second derivative.
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Step 14.1
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because sine is negative in the third quadrant.
Step 14.2
The exact value of is .
Step 14.3
Cancel the common factor of .
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Step 14.3.1
Move the leading negative in into the numerator.
Step 14.3.2
Factor out of .
Step 14.3.3
Cancel the common factor.
Step 14.3.4
Rewrite the expression.
Step 14.4
Multiply.
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Step 14.4.1
Multiply by .
Step 14.4.2
Multiply by .
Step 15
is a local minimum because the value of the second derivative is positive. This is referred to as the second derivative test.
is a local minimum
Step 16
Find the y-value when .
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Step 16.1
Replace the variable with in the expression.
Step 16.2
Simplify the result.
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Step 16.2.1
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 third quadrant.
Step 16.2.2
The exact value of is .
Step 16.2.3
Combine and .
Step 16.2.4
The final answer is .
Step 17
These are the local extrema for .
is a local maxima
is a local minima
Step 18