Question

which of the following are identities? (more than one)
a. sin(x-PI) = -sinx
b. sin(x+y) - sin(x-y) = 2cosxsiny
c. cos(x+y)+cos(x-y) = cos^2 x - sin ^2 y
D.cos(x+y)+cos(x-y) = 2cosxcosy

Answer 1

(a) is one

Answer 2

and (b)

Answer 3

do you know the identities for sin and cos of compound angles?
i used 2 of these to check b out

Answer 4

sin(x+y) - sin(x-y) = sinxcosy + cosxsiny - ( sinxcosy - cosxsiny)
= 2cosx siny

Answer 5

you can check out c and d in a similar way

Answer 6

okay i can't do c bc its ^2 ...and my calc won't do that

Answer 7

the last one is true. the third one i dont think is

Answer 8

ty