I have a general idea about it, but I can't calculate it correctly ...

Question: Find a cubic function, in the form below, that has a local maximum value of 3 at -4 and a local minimum value of 0 at 3.
f (x) = ax3 + bx2 + cx + d

What I am doing now:
f(-4)=3---64a+16b-4c+d=3
f(3)=0---27a+9b+3c+d=0
f'(-4)=f'(3)=0---a=b
f'(x)=3ax^2+2bx+c

Question

I have a general idea about it, but I can't calculate it correctly ...

Question: Find a cubic function, in the form below, that has a local maximum value of 3 at -4 and a local minimum value of 0 at 3.
f (x) = ax3 + bx2 + cx + d


What I am doing now:
f(-4)=3---64a+16b-4c+d=3
f(3)=0---27a+9b+3c+d=0
f'(-4)=f'(3)=0---a=b
f'(x)=3ax^2+2bx+c

anonymous · Answer

and I got c=-12a and d=84a
a=196/3

I think they're wrong..

anonymous · Answer

f (x) = ax^3 + bx^2 + cx + d

shubhamsrg · Answer

how do you get a=b ? o.O
you should be getting 3a=2b..
please recheck..

anonymous · Answer

yeeeahhh !!! I got it !!! damnnn.. I always make such stupid mistakes!!! thank you soooo MUCH !

shubhamsrg · Answer

glad to help ^_^