SOLUTION: please help determine where the function is increasing and where it is decreasing. f(x) = -x^2 - 8x

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: please help determine where the function is increasing and where it is decreasing. f(x) = -x^2 - 8x      Log On


   

Question 616971: please help determine where the function is increasing and where it is decreasing.
f(x) = -x^2 - 8x
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi, 

where the function is increasing and where it is decreasing.

f(x) = -x^2 - 8x

Taking the 1st derivative:

 f'(x) =  -2x - 8   

 f'(x) > 0 when x < -4  and  f'(x)< 0 when x > -4

function is increasing when x < -4 and  is decreasing when x >-4