tolong dibantu ya. ............

Bab Trigonometri
Matematika SMA Kelas X

tan A = -1/3 → y/x
π/2 < x < π (kuadran II)

r = √(x² + y²)
r = √(3² + (-1)²)
r = √(9 + 1)
r = √10

sin A . cos A
= y/r . x/r
= 1/√10 . (-3)/√10
= -3/10