Question

已知A(-1,3),B(2,2),C(1,-1),求三角形ABC的面积要详细的过程谢谢!

Answer 1

AC的方程: (y + 1)/(3 + 1) = (x - 1)/(-1 - 1), 2x +y - 1 = 0

B与AC的距离h = |2*2 + 1*2 -1|/√(2² + 1²) = √5

AC = √[(-1 -1)² + (3 + 1)²] = 2√5

S = (1/2)*AC*h = (1/2)*2√5*√5 = 5