直線(xiàn)y=kx+b斜率為k, 其垂線(xiàn)斜率為-1/k
過(guò)P的垂線(xiàn)方程為: y - n = (-1/k)(x - m)
與y = kx + b聯(lián)立得交點(diǎn)為Q((kn - kb + m)/(k² + 1), (k²n +km + b)/(k² + 1))
Q為PP'的中點(diǎn), P'(p, q)
(m + p)/2 = (kn - kb + m)/(k² + 1), p = 2(kn - kb + m)/(k² + 1) - m = (2kn - 2kb + m - k²m)/(k² + 1)
(n + q)/2 = (k²n +km + b)/(k² + 1), q = 2(k²n +km + b)/(k² + 1) - n = (k²n +2km + 2b - n)/(k² + 1)
P'((2kn - 2kb + m - k²m)/(k² + 1), (k²n +2km + 2b - n)/(k² + 1))y = kx + b, k就是斜率。它是x增加一個(gè)單位時(shí)y的變化。