设直线l斜率k, 方程y - 1/2 = k(x - 1), x = y/k + 1 - 1/(2k)
y² = 4y/k + 4 -2/k
ky² - 4y + 2k - 4 = 0
y₁ + y₂ = 4/k
M纵坐标1/2 = (y₁ + y₂)/2
y₁ + y₂ = 4/k = 1
k = 4
AB的方程: y - 1/2 = 4(x - 1)
y = 4x - 7/2
不对啊 此题为选择题 没有这个选项 啊
A。x-4y-1=0
B,8x-2y-7=0
C。x+4y-3=0
D。8x+2y-9=0
再算算啊