Diketahui tan A = -1/3 dengan π/2 < A < π,maka nilai sin A × cos A =

tanA = -1/3 ---> y = 1 dan x = -3 (kuadran II)
r = √(y² + x²) = √(1² + (-3)²) = √10
sinA = y/r = 1/√10 = (1/10)√10
cosA = x/r = -3/√10 = -(3/10)√10
sinA cosA = (1/10)√10 . -(3/10)√10 = -3/10