已知a的平方+b的平方-2a+4b+5=0,求2a-b的值
人气：431 ℃ 时间：2019-11-11 13:16:37
解答
a²+b²-2a+4b+5=0
(a²-2a+1)+(b²+4b+4)=0
(a-1)²+(b+2)²=0
平方项恒非负,两非负项之和=0,两非负项分别=0
a-1=0 a=1
b+2=0 b=-2
2a-b=2×1-(-2)=4
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