Question

Find the critical values of P(x)

p(x)= (28+x)(8-x/4)

the answer was p=244-7x+8x-x^2/4

p=-x^2/4 + x + 244
p'= -x/2 +1 = 0
X=2
My question is, I do not understand how they got -7x + 8x at the beginning. I know (28)(8)=244 but I do not get the rest.

Answer 1

Use FOIL:
(28+x)(8-x/4)
=28*8 -28*x/4 + 8*x -x*x/4
=244 -7x + 8x -x²/4
=244 + x -x²/4

and the rest follows.

Answer 2

Oh I see. I made a mistake with the 28 (x/4). Thanks!