Diket cos a = 3/5, cos b = -15/17. a sudut lancip, b sudut tumpul. Tentukan : a. Sin (a+b) b. Sin (a-b)

a lancip, jadi sin(a) dan cos(a) positif

sin(a)=akar(1-cos2(a))
=akar(1-(3/5) kuadrat))
=akar(1-9/25)
=4/5

b tumpul, jadi sin(b) positif, cos(b)<0

sin(b)=akar(1-cos2(b))
=akar(1-(-15/17) kuadrat)
=8/17

sin(a+b)=sin(a)cos(b)+sin(b)cos(a)
=(4/5)*(-15/17)+(8/17)*(3/5)
=-36/85

sin(a-b)=sin(a)cos(b) - sin(b)cos(a)
=(4/5)*(-15/17) - (8/17)*(3/5)
=-84/85