綾 3個月以前 AB中點座標((a+b)/2, 2) 2[(a+b)/2] + 2 = 4 a + b = 2⋯① 令直線AB:x - 2y = c a - 2 = c⋯② b - 6 = c⋯③ ②-③ a - b = -4⋯④ ①+④ 2a = -2 a = -1 b = 3 2a + b = 1 留言