问题
解答题
解方程：x2＋2x-15＝0.
答案
解法一：a="1," b="2," c="-15,"
>0. …………………………………………2分
…………………………………………3分
∴x1 =" 3," x2 =" -5. " …………………………………………5分
解法二：( x -3 )( x+5 )＝0， …………………………………………3分
∴x1 =" 3," x2 =" -5. " …………………………………………5分
解法三：x2＋2x＝15，
x2＋2x+1＝15+1. …………………………………………2分
(x＋1)2＝42. …………………………………………3分
x＋1＝±4.
∴x1 =" 3," x2 =" -5. " …………………………………………5