Posted by sayan on .
Angle a lies in the second quadran and angle b lies in the third quadrant such that cos a = 3/5 and tan b = 24/7. Determine an exact value for cos (a+b), sin(ab)

maths 
Steve,
sin a = 4/5
sin b = 24/25
cos b = 7/25
cos(a+b) = cosa*cosbsina*sinb
= (3/5)(7/25)  (4/5)(24/25)
= 21/125 + 96/125
= 117/125
now apply the formula for sin(ab) the same way.