Question 495687
Find the exact value of the expression: 
sin (3pi/4) cos (5pi/6) - cos(3pi/4) sin (5pi/6)
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Addition formula for sin function:
sin(s-t)=sin s cos t - cos s sin t
For given function:
s=3π/4
t=5π/6
..
sin (3π/4) cos (5π/6) - cos(3π/4) sin (5π/6)
=sin(s-t)
=sin(3π/4-5π/6)
=sin(9π/12-10π/12)
=sin(-π/12)=-0.2588