math
posted by i need help .
sin a=3/5, a lies on quadrant 1 and sin b=5/13, b lies on quadrant 2. Find cos(a+b)

cos(a+b)=sinasinbcosa*cosb
sina is given, so cosa=4/5
sinb is given so cos b=12/13
posted by i need help .
sin a=3/5, a lies on quadrant 1 and sin b=5/13, b lies on quadrant 2. Find cos(a+b)
cos(a+b)=sinasinbcosa*cosb
sina is given, so cosa=4/5
sinb is given so cos b=12/13