Question

simplify:
cos(180°+x)cos(x-180°) - sin(180°+x)sin(x-180°)

Answer 1

Scroll down to below example 7
in
http://www.cliffsnotes.com/study_guide/Addition-Identities.topicArticleId-11658,articleId-11610.html

for how to simplify these expressions. what do you get ?

Answer 2

can u just please put the answer step by step as to how u got it, I learn better that way, thanks

Answer 3

Did you see the section after example 7 ?

Answer 4

oh got it thanks can u help me with 1 last 1 i promise this is it.
verify that 2tanxcos^2x=sin2x
Thanks!!

Answer 5

change tanx to sin(x)/cos(x) and simplify the left side
use the formula for sin(x+x) (see the link for the formala) for the right side

Answer 6

2sinxcos^2x=sin2x is what i get, what do i do after??

Answer 7

you did not do that correctly
tanx = sin(x)/cos(x)

Answer 8

I know and I canceled it out with the cos^2x which got me 2sinxcosx

Answer 9

ok, now you have
2 sinx cos x = sin2x

write sin 2x as sin(x+x) now use the formula for sin(x+x)

Answer 10

Ohhh I see it, thanks!! :-)