Posted by **jj reddick** on Monday, October 25, 2010 at 4:15am.

determine an exact expression for the trigonometric function sin(13pi/12).

- trig -
**jai**, Monday, October 25, 2010 at 8:34am
note that 13pi/12 is also 195 degrees, which can be expressed as difference of two angles, 240 - 45:

sin(13pi/12) = sin(195) = sin(240-45)

*expanding this,

sin(240)cos(45)-cos(240)sin(45)

(-sqrt(3)/2)(sqrt(2)/2)-(-1/2)(sqrt(2)/2)

(-sqrt(6)/4)+(sqrt(2)/4)

therefore:

{[sqrt(2)-sqrt(6)]/4}

so there,, :)

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