Question

Help PLEASE !
1. find the exact value of the sin2x if the cosx=5/7
3. find the exact value of the tan2x if the cosx=5/7
4. find the exact solutions in the interval [0,2pi} for sin2xcosx=sinx
5.rewrite the following expression using double angle formulas.
-6cos^2x-3+6sinxcosx

Answer 1

Remember SOH CAH TOA? Apply that here, and to the rest of all your trig and you will be saved most of the time! =D

Answer 2

I'm assuming you mean sin^2(x) and tan^2(x) as well.

Answer 3

for the first two calculate sinx and then use sin2x= 2sinxcosx to find sin 2x. use tan2x=2tanx/1-tan^2x to calculate tan 2x

u can simplify the 3 rd one
like this sin2xcosx=sinx
2sinxcosxcosx= sinx
sinx(2cos^x-1)=0
sinx = 0 2cos^2x-1=0
cosx= +1/square2 or -1/squared2