点(x0,y0)到直线(ax+by+c=0)公式
d =|ax0+by0+c|/√(a^2+b^2)
设 P 点坐标为 (x0,0),则
|x0| = |ax0+by0+c|/√(a^2+b^2) = |4x0 -8|/√(4^2+3^2) = |4x0 - 8|/5
5|x0| = 4|x0 - 2|
两边平方
25 x0^2 = 16(x0^2 -4x0 + 4)
9x0^2 + 64x0 - 64 = 0
(9x0 -8)(x0 + 8) = 0
x0 = 8/9
和
x0 = -8