Posted by sayan on Wednesday, April 11, 2012 at 11:56pm.
sin a = 4/5
sin b = -24/25
cos b = -7/25
cos(a+b) = cosa*cosb-sina*sinb
= (-3/5)(-7/25) - (4/5)(-24/25)
= 21/125 + 96/125
= 117/125
now apply the formula for sin(a-b) the same way.
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