已知直线l1:y=x+1,l2:y=-x-1,l3:y=-2x+4
l1与l2交于A(-1,0)
l1与l3交于B(1,2)
l2与l3交于C(5,-6)
AB = √[2²+2²] = 2√2
C与l1距离为1/√2
所以,
SABC = 2√2 * 1/√2 * (0.5) = 1
希望采纳~~~