ada yang tau caranya?

a.
L = 1/2 .AC.BC.sin C
L = 1/2.7.13.sin 135
L = 1/2.7.13.1/2√2
L = 91/4 √2

b.
L = 1/2.AB.AC.sin A
L = 1/2x9x7xsin 30°
L = 63/2 x 1/2
L = 63/4

c. AB= 13,AC= 4,BC = 15
s = 13+4+15/2 = 32/2 = 16

L = √s(s-a)(s-b)(s-c)
L = √16(16-13)(16-4)(16-15)
L = √16.3.12.1
L = √576
L = 24 cm^2

d. sudut B = 180° - (60°+30°) = 180° - 90° = 90°

L = ac^2 sin A.sin C/2.sin B
L = 8^2.sin 30°.sin 60°/ 2.sin 90°
L = 64.(1/2).(1/2√3)/2.1
L = 16√3/2
L = 8√3 cm^2