Determine whether a function is positive or negative? (1 Viewer)

[matreha]

Hi everyone

I am stuck on a maths question:

Determine whether f'(2) is positive or negative:
a) f(x) = x^2 - 7x

How do I solve it?

Please help! Thanks

 

[Kaido]

differentiate f(x) to get f'(x)=2x-7
sub in x=2 in f'(x) to get: f'(2)=2(2)-7=-3 (which is negative)

 

[matreha]

Thanks for replying! However when differentiating the 7 part of the equation doesn't it just go away?

i.e. f(x) = x^2 - 7 so f'(x) = 2x

 

[matreha]

Oh wait, I get it now! Thank you