2分之3x+y=14分之5x-y 两边同时乘以14 7(3x+y) = (5x-y) 21x + 7y = 5x-y 16x = -8y 2x = -y y = -2x 2x-3y+7 = 2x - 3*(-2x) + 7 = 2x + 6x + 7 = 8x + 7 或者2x-3y+7 = 8x+7 = 8*(-0.5y)+7 = -4y+7