Find included angle of a triangle knowing: area = 15 cm^2 sides 5 cm and 8 cm.
Use the trig identity: S = 1/2 bc.sin A
S –> Area = 15 ; side b = 5; side c = 8; find sin A
##sin A = (2S)/(bc) = (2(15))/(5(8)) = 30/40 = 3/4 = 0.75##
Calculator –> ##A = 48.59## deg or ##A = 180 – 48.59 = 131.41## deg