How do you find all critical point and determine the min, max and inflection given f(x)=x^2-8x-10f(x)=x28x10?

1 Answer
Oct 16, 2016

At x=4x=4 is a minimum only

Explanation:

f(x)=x^2-8x-10f(x)=x28x10
Differentiating with respect to x, f'(x)=2x-8
Differentiating once more, f''(x)=2 which is >0 so we are expecting a minimum
When f'(x)=0 => 2x-8=0 =>x=4
When x<4, f'(x) <0
and when x>4, f'(x)>0
So we have a minimum
Check
f(3)=3*3-8*3-10=-25
f(5)=5*5-8*5-10 =-25
and f(4)=4*4-8*4-10=-26
So we have a min. only