Posted by **rebecca** on Thursday, October 21, 2010 at 10:44am.

how do you establish the identity of cos(3pi/2+0)=sin0

- trig -
**Reiny**, Thursday, October 21, 2010 at 11:15am
To me this appears to be a silly question, if your 0 is indeed a zero.

Why even write it as (3π/2 + 0)

it would simply be cos 3π/2

and you should know that cos 3π/2 = 0 which is also the value of the right side.

End of problem.

- trig -
**jai**, Saturday, October 23, 2010 at 5:47am
is the "0" in the problem, the angle theta? if it is,

cos(3pi/2+[theta]) = sin [theta]

*expand cos(3pi/2+[theta]),

cos(3pi/2)cos(theta) - sin(3pi/2)sin(theta) = sin [theta]

*cos(3pi/2) = 0 and sin(3pi/2) = -1, thus:

-(-sin [theta]) = sin [theta]

sin [theta] = sin [theta]

so there,, :)

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