tolong dong soal mtk ...!

Diket :
panjang a=7 ; b =3 ; c = 5
Ditanya :
Sin A ?
Jawab :
a²=b²+c²-2bc.Cos A
7²=3²+5²-2.3.5.Cos A
30.Cos A = -15
Cos A = -½
A = 240
Sin A = sin 240 = -½√3