✔ 最佳答案
x^2 - 9x + 9 = 0
x = -(-9) ± √ (-9)^2 -4(1)(9) / 2(1)
x= 9 ± √ 45 /2
2012-12-27 15:38:07 補充:
上面係2次公式
2012-12-27 15:41:31 補充:
配方法:
x^2 - 9x + 9 = 0
x^2 - 9x + (9/2)^2 - (9/2)^2 +9 =0
( x + 9/2 )^2 - 45/4 = 0
2012-12-27 15:50:54 補充:
( x + 9/2 )^2 = 45/4
x + 9/2 = ±√45/4
x= 9 ± √ 45 /2