Calculus Examples

Find the Local Maxima and Minima f(x)=5x+cos(2x+1)
f(x)=5x+cos(2x+1)f(x)=5x+cos(2x+1)
Step 1
Find the first derivative of the function.
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Step 1.1
By the Sum Rule, the derivative of 5x+cos(2x+1)5x+cos(2x+1) with respect to xx is ddx[5x]+ddx[cos(2x+1)]ddx[5x]+ddx[cos(2x+1)].
ddx[5x]+ddx[cos(2x+1)]ddx[5x]+ddx[cos(2x+1)]
Step 1.2
Evaluate ddx[5x]ddx[5x].
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Step 1.2.1
Since 55 is constant with respect to xx, the derivative of 5x5x with respect to xx is 5ddx[x]5ddx[x].
5ddx[x]+ddx[cos(2x+1)]5ddx[x]+ddx[cos(2x+1)]
Step 1.2.2
Differentiate using the Power Rule which states that ddx[xn]ddx[xn] is nxn-1nxn1 where n=1n=1.
51+ddx[cos(2x+1)]51+ddx[cos(2x+1)]
Step 1.2.3
Multiply 55 by 11.
5+ddx[cos(2x+1)]5+ddx[cos(2x+1)]
5+ddx[cos(2x+1)]5+ddx[cos(2x+1)]
Step 1.3
Evaluate ddx[cos(2x+1)]ddx[cos(2x+1)].
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Step 1.3.1
Differentiate using the chain rule, which states that ddx[f(g(x))]ddx[f(g(x))] is f(g(x))g(x)f'(g(x))g'(x) where f(x)=cos(x)f(x)=cos(x) and g(x)=2x+1g(x)=2x+1.
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Step 1.3.1.1
To apply the Chain Rule, set uu as 2x+12x+1.
5+ddu[cos(u)]ddx[2x+1]5+ddu[cos(u)]ddx[2x+1]
Step 1.3.1.2
The derivative of cos(u)cos(u) with respect to uu is -sin(u)sin(u).
5-sin(u)ddx[2x+1]5sin(u)ddx[2x+1]
Step 1.3.1.3
Replace all occurrences of uu with 2x+12x+1.
5-sin(2x+1)ddx[2x+1]5sin(2x+1)ddx[2x+1]
5-sin(2x+1)ddx[2x+1]5sin(2x+1)ddx[2x+1]
Step 1.3.2
By the Sum Rule, the derivative of 2x+12x+1 with respect to xx is ddx[2x]+ddx[1]ddx[2x]+ddx[1].
5-sin(2x+1)(ddx[2x]+ddx[1])5sin(2x+1)(ddx[2x]+ddx[1])
Step 1.3.3
Since 22 is constant with respect to xx, the derivative of 2x2x with respect to xx is 2ddx[x]2ddx[x].
5-sin(2x+1)(2ddx[x]+ddx[1])5sin(2x+1)(2ddx[x]+ddx[1])
Step 1.3.4
Differentiate using the Power Rule which states that ddx[xn]ddx[xn] is nxn-1nxn1 where n=1n=1.
5-sin(2x+1)(21+ddx[1])5sin(2x+1)(21+ddx[1])
Step 1.3.5
Since 11 is constant with respect to xx, the derivative of 11 with respect to xx is 00.
5-sin(2x+1)(21+0)5sin(2x+1)(21+0)
Step 1.3.6
Multiply 22 by 11.
5-sin(2x+1)(2+0)5sin(2x+1)(2+0)
Step 1.3.7
Add 22 and 00.
5-sin(2x+1)25sin(2x+1)2
Step 1.3.8
Multiply 22 by -11.
5-2sin(2x+1)52sin(2x+1)
5-2sin(2x+1)52sin(2x+1)
5-2sin(2x+1)52sin(2x+1)
Step 2
Find the second derivative of the function.
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Step 2.1
Differentiate.
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Step 2.1.1
By the Sum Rule, the derivative of 5-2sin(2x+1)52sin(2x+1) with respect to xx is ddx[5]+ddx[-2sin(2x+1)]ddx[5]+ddx[2sin(2x+1)].
f′′(x)=ddx(5)+ddx(-2sin(2x+1))f''(x)=ddx(5)+ddx(2sin(2x+1))
Step 2.1.2
Since 55 is constant with respect to xx, the derivative of 55 with respect to xx is 00.
f′′(x)=0+ddx(-2sin(2x+1))f''(x)=0+ddx(2sin(2x+1))
f′′(x)=0+ddx(-2sin(2x+1))f''(x)=0+ddx(2sin(2x+1))
Step 2.2
Evaluate ddx[-2sin(2x+1)]ddx[2sin(2x+1)].
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Step 2.2.1
Since -22 is constant with respect to xx, the derivative of -2sin(2x+1)2sin(2x+1) with respect to xx is -2ddx[sin(2x+1)]2ddx[sin(2x+1)].
f′′(x)=0-2ddxsin(2x+1)f''(x)=02ddxsin(2x+1)
Step 2.2.2
Differentiate using the chain rule, which states that ddx[f(g(x))]ddx[f(g(x))] is f(g(x))g(x)f'(g(x))g'(x) where f(x)=sin(x)f(x)=sin(x) and g(x)=2x+1g(x)=2x+1.
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Step 2.2.2.1
To apply the Chain Rule, set uu as 2x+12x+1.
f′′(x)=0-2(ddu(sin(u))ddx(2x+1))f''(x)=02(ddu(sin(u))ddx(2x+1))
Step 2.2.2.2
The derivative of sin(u)sin(u) with respect to uu is cos(u)cos(u).
f′′(x)=0-2(cos(u)ddx(2x+1))f''(x)=02(cos(u)ddx(2x+1))
Step 2.2.2.3
Replace all occurrences of uu with 2x+12x+1.
f′′(x)=0-2(cos(2x+1)ddx(2x+1))f''(x)=02(cos(2x+1)ddx(2x+1))
f′′(x)=0-2(cos(2x+1)ddx(2x+1))f''(x)=02(cos(2x+1)ddx(2x+1))
Step 2.2.3
By the Sum Rule, the derivative of 2x+12x+1 with respect to xx is ddx[2x]+ddx[1]ddx[2x]+ddx[1].
f′′(x)=0-2(cos(2x+1)(ddx(2x)+ddx(1)))f''(x)=02(cos(2x+1)(ddx(2x)+ddx(1)))
Step 2.2.4
Since 22 is constant with respect to xx, the derivative of 2x2x with respect to xx is 2ddx[x]2ddx[x].
f′′(x)=0-2(cos(2x+1)(2ddx(x)+ddx(1)))f''(x)=02(cos(2x+1)(2ddx(x)+ddx(1)))
Step 2.2.5
Differentiate using the Power Rule which states that ddx[xn]ddx[xn] is nxn-1nxn1 where n=1n=1.
f′′(x)=0-2(cos(2x+1)(21+ddx(1)))f''(x)=02(cos(2x+1)(21+ddx(1)))
Step 2.2.6
Since 11 is constant with respect to xx, the derivative of 11 with respect to xx is 00.
f′′(x)=0-2(cos(2x+1)(21+0))f''(x)=02(cos(2x+1)(21+0))
Step 2.2.7
Multiply 22 by 11.
f′′(x)=0-2(cos(2x+1)(2+0))f''(x)=02(cos(2x+1)(2+0))
Step 2.2.8
Add 22 and 00.
f′′(x)=0-2(cos(2x+1)2)f''(x)=02(cos(2x+1)2)
Step 2.2.9
Move 22 to the left of cos(2x+1)cos(2x+1).
f′′(x)=0-2(2cos(2x+1))f''(x)=02(2cos(2x+1))
Step 2.2.10
Multiply 22 by -22.
f′′(x)=0-4cos(2x+1)f''(x)=04cos(2x+1)
f′′(x)=0-4cos(2x+1)f''(x)=04cos(2x+1)
Step 2.3
Subtract 4cos(2x+1)4cos(2x+1) from 00.
f′′(x)=-4cos(2x+1)f''(x)=4cos(2x+1)
f′′(x)=-4cos(2x+1)f''(x)=4cos(2x+1)
Step 3
To find the local maximum and minimum values of the function, set the derivative equal to 00 and solve.
5-2sin(2x+1)=052sin(2x+1)=0
Step 4
Subtract 55 from both sides of the equation.
-2sin(2x+1)=-52sin(2x+1)=5
Step 5
Divide each term in -2sin(2x+1)=-52sin(2x+1)=5 by -22 and simplify.
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Step 5.1
Divide each term in -2sin(2x+1)=-52sin(2x+1)=5 by -22.
-2sin(2x+1)-2=-5-22sin(2x+1)2=52
Step 5.2
Simplify the left side.
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Step 5.2.1
Cancel the common factor of -22.
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Step 5.2.1.1
Cancel the common factor.
-2sin(2x+1)-2=-5-2
Step 5.2.1.2
Divide sin(2x+1) by 1.
sin(2x+1)=-5-2
sin(2x+1)=-5-2
sin(2x+1)=-5-2
Step 5.3
Simplify the right side.
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Step 5.3.1
Dividing two negative values results in a positive value.
sin(2x+1)=52
sin(2x+1)=52
sin(2x+1)=52
Step 6
The range of sine is -1y1. Since 52 does not fall in this range, there is no solution.
No solution
Step 7
Evaluate the second derivative at x=. If the second derivative is positive, then this is a local minimum. If it is negative, then this is a local maximum.
-4cos(2+1)
Step 8
Evaluate the second derivative.
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Step 8.1
Add 2 and 1.
-4cos(3)
Step 8.2
Evaluate cos(3).
-40.99862953
Step 8.3
Multiply -4 by 0.99862953.
-3.99451813
-3.99451813
Step 9
x= is a local maximum because the value of the second derivative is negative. This is referred to as the second derivative test.
x= is a local maximum
Step 10
These are the local extrema for f(x)=5x+cos(2x+1).
(,isa(local)(maximum)) is a local maxima
Step 11
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