a dan b sudut lancip sin a = 4/5 sin b = 12/13 maka tan(a+b) =

sin a = 4/5
sisi depan 4
sisi miring 5
maka sisi samping = 3 (pakai pitagoras)
tan a = 4/3

sin b = 12/13
sisi depan 12
sisi miring 13
sisi samping 5
tan b = 12/5

tan (a+b) = (tan a + tan b) / (1 - tan a tan b)
= (4/3 + 12/5) / (1 - (4/3)(12/5))
= (20/15 + 36/15) / (15/15 - 48/15)
= (56/15) / (-33/15)
= (56/15) / (-15/33)
= -56/33