前两题会运用
if a^2 - b^2 = 0, then (a+b)(a-b) = 0 的公式
(1)
x的平方 -6x-18=0
写成
x^2 - 6x + 9 - 27 = 0
(x-3)^2 - 27 = 0
(x-3+根号[27])(x-3-根号[27]) = 0
(2)
x的平方 +2(x-1)=0
写成
x^2 + 2x + 1 - 3 = 0
(x+1)^2 - 3 = 0
(x+1 +根号[3])(x+1 -根号[3]) = 0
(3)
x的平方 -2x-35=0
(x+5)*(x-7) = 0
x = -5 or x = 7
(4)
7x(5x+2)=6x(5x+2)
5x^2 + 2x = 0
x(5x + 2) = 0
x = 0 or x = -2/5