Question

solve for the second derivative and set to zero

f"(x) = ((x^2-4)*sin(2x)- [(2x)(1+cos^2(x))]/ ((1+cos^2(x))^2)

i don't know how to set it to zero and solve i get this:

(x^2-4)(sin(2x))= (2x)(1+cos^2(x))

thanks for help

Answer 1

I reduced your expression to

(x^2-4)*sin(2x)- (2x)/(1+cos^2(x))=0
(x^2-4)*sin(2x) = (2x)/(1+cos^2(x))

(x^2-4)*sin(2x)(1+cos^2(x)) = 2x

which is not what we are to get.

I noticed that the very first and very last brackets are not really needed.
Perhaps some of those brackets are misplaced.