Question

prove
cos(3pi/2 )-A) =-sin A
i am no good at these

Answer 1

i wrote you a hint before :| why did you open a new one

use the identity:

cos(a+b) = cos(a)cos(b) - sin(a)sin(b)

and another hint cos(3pi/2) = 0

Answer 2

i dont understand what to do?

Answer 3

cos(3pi/2-A)
let 3pi/2 = x , -A = y

now use
cos(x+y) = cos(x)cos(y) - sin(x)sin(y)
and see if you get -sin(A)

Answer 4

cos(a+b) is short hand. You match the letter a to the first term in your problem and match the letter b to the 2nd term

it might be easier if you use
cos(a-b)= cos(a)cos(b)+sin(a)sin(b)

Answer 5

got it thx

Answer 6

took me a while didnt think to use my unit circle!