已知关于x的一元二次方程x 2 +(m+3)x+m+1=0.(1)求证:无论m取何值,原方程总有两个不相等的实数根:

2024-11-13 20:39:16
推荐回答(1个)
回答1:

(1)证明:∵△=(m+3) 2 ﹣4(m+1)
=(m+1) 2 +4
∴无论m取何值,(m+1) 2 +4恒大于0
∴原方程总有两个不相等的实数根
(2)∵x 1 ,x 2 是原方程的两根
∴x 1 +x 2 =﹣(m+3),x 1 x 2 =m+1
∵|x 1 ﹣x 2 |=2
∴(x 1 ﹣x 2 2 =(2 2
∴(x 1 +x 2 2 ﹣4x 1 x 2 =8
∴[﹣(m+3)] 2 ﹣4(m+1)=8
∴m 2 +2m﹣3=0
解得:m 1 =﹣3,m 2 =1
当m=﹣3时,原方程化为:x 2 ﹣2=0
解得:x 1 = ,x 2 =﹣ …11分
当m=1时,原方程化为:x 2 +4x+2=0
解得:x 1 =﹣2+ ,x 2 =﹣2﹣


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