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Sign analyses for second derivatives: Repeat the instructions of the previous block of problems, except find sign intervals for the second derivative f''instead of the first derivative.

f(x)=x23x

Short Answer

Expert verified

The second derivative of the given function is the local maximum at x=-1.8,and a local minimum at x=0.

Step by step solution

01

Step 1. Given Information.

The given function isf(x)=x23x.

02

Step 2. Find the second derivative. 

To find the second derivative, first, we find the first derivative then the second.

So,

f(x)=x23xf'(x)=x23xln3+2x3xf''(x)=x2ln33xln3+(2x)3xln3+2x3xln3+23xf''(x)=x2ln33xln3+4x3xln3+23x

03

Step 3. Find sign intervals for the second derivative. 

To find the sign intervals let's find the critical points from the first derivative.

So,

f'(x)=0x23xln3+2x3x=0x3x(xln3+2)=0x=0andx=−2ln3x=−21.09x=−1.8

Thus, the critical points arex=0andx=−1.8.

Now, at x=0,f''(x)>0and atx=-1.8,f''(x)<0.

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