Exact values of sin(30) and cos(3pi/2)

How can I work out exact values for trig functions like sin(30) and cos(3pi/2)?

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For simple expressions, use trigonometric/complex identities to reduce to terms you already know. For more complicated expressions, use series, ie., Taylor or Euler's expansions.

cscott said:
How can I work out exact values for trig functions like sin(30) and cos(3pi/2)?
Like the decimal values? Without a calculator?

I would just draw out the triangle and leave the answer in the exact radical form, like in your first example. But $\cos{\frac{3\pi}{2}}$ is 0 so that should be easy.

Ah thanks.