Originally Posted by

**euphmorning** Just trying to understand the answer in my book here...

given that cos(2x) = 2cos^2 x -1

then:

cos^2 x = 1/2(cos(2x) + 1). agreed.

my problem comes upon integrating cos^2 x..

i get thus far:

cos^2 x dx = 1/2(cos(2x) + 1).

=1/2(1/2 sin(2x) + x) + c

agreed. it is the next bit that is throwing me off..

distributing out the 1/2 i get:

1/4sin(2x) + 2x) + c

i'm sure i'm missing something terribly obvious here, but where does the the extra x (2x term) pop up from ?

kind thankyous in advance!