If f(x) is decreasing for every x > 5, then which choice is not a possibility for f'(x)?


a) f'(x) = x-5 

b) f'(x) = 5-x 

c) f'(x) = -x^2+10x-25 

d) f'(x) = -5 


I chose a, am I correct?

Julius  Apr 11, 2018

Correct, Julius  !!!!


For all x > 5,   x - 5 will be positive, thus increasing.....


Also  [ don't worry about how I arrived at this ] ....if  x - 5  is the derivative, then  (1/2)x^2 - 5x + some constant   is the parent function....as shown here, no matter the added constant, this function always increases when x > 5





cool cool cool

CPhill  Apr 11, 2018

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