x+2y-3=0, x = 3-2y
代入x²+y²+x-6y+m=0, 5y² - 20y + 12+m = 0
△=400-4*5*(12+m) = 20(8-m)
y1 = (20 + √△)/10 = 2 + (√△)/10, x1 = 3 - 2(2 + √△/10) = -1 -(√△)/5
y2 = (20 - √△)/10 = 2 - (√△)/10, x2 = 3 - 2(2 - √△/10) = -1 +(√△)/5
P(-1 -(√△)/5, 2 + (√△)/10)
Q(-1 +(√△)/5, 2 - (√△)/10)
OP的斜率k1 = [2 + (√△)/10]/[-1 -(√△)/5]
OQ的斜率k2 = [2 - (√△)/10]/[-1 +(√△)/5]
OP垂直于OQ, k1*k2= -1
{[2 + (√△)/10]/[-1 -(√△)/5] }* {[2 - (√△)/10]/[-1 +(√△)/5]} = -1
(4 - △/100)/(1 - △/25)= -1
△=100
20(8-m)=100
m=3为什么网上有这么多种不同答案？你确定3是对的吗？我看不出我做的有任何问题。m = 3, x²+y²+x-6y+m=0变为x²+y²+x-6y+3=0代入x = 3-2y并简化得y² - 4y + 3 = 0y1 = 1, y2 = 3x1 = 1, x2 = -3交点为P（1,1），Q(-3, 3)OP的斜率为1，OQ的斜率为-1，二者垂直。