Question

prove the identity. show all work. cos(x-pi/2)=sin x

Answer 1

cos (A+B) = ?

Answer 2

huh?

Answer 3

cos (A+B) =cos A cos B - sin A sin B
now put A=x and B=pi/2

Answer 4

but its cos (x-pi/2) not addition?

Answer 5

sorry, B = -pi/2
or u can use cos (A-B) = cos A cos B +sin A sin B

Answer 6

ohh ok so cos xcospi/2+sin x cospi/2

Answer 7

cos x cos pi/2+sin x sin pi/2
now what is cos pi/2 and sin pi/2 = ?

Answer 8

0

Answer 9

sin =1

Answer 10

so plug those values in, what u get ?

Answer 11

so the rhs cancels ans ur left with 1 *sin x which is equal to sinx

Answer 12

thats correct :)

Answer 13

cos x cos pi/2+sin x sin pi/2 = cos x (0)+sin x (1) = sin x

Answer 14

yay thank you only a few more questions and im done

Answer 15

great ! bring it on ...