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> (1)计算:1318-612+212(2)用配方法解方程:x2-4x-5=0.-数学
(1)计算:1318-612+212(2)用配方法解方程:x2-4x-5=0.-数学
题目简介
(1)计算:1318-612+212(2)用配方法解方程:x2-4x-5=0.-数学
题目详情
(1)计算:
1
3
18
-6
1
2
+2
12
(2)用配方法解方程:x
2
-4x-5=0.
题型:解答题
难度:中档
来源:不详
答案
(1)原式=
class="stub"1
3
×3
2
-6×
2
2
+2×2
3
=
2
-3
2
+4
3
=-2
2
+4
3
;
(2)由原方程移项,可得
x2-4x=5,
等式的两边同时加上一次项系数-4的一半的平方,得
x2-4x+22=9,
配方,得
(x-2)2=9,
开方,得
x-2=±3,
解得,x1=5,x2=-1
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题目简介
(1)计算:1318-612+212(2)用配方法解方程:x2-4x-5=0.-数学
题目详情
(2)用配方法解方程:x2-4x-5=0.
答案
(2)由原方程移项,可得
x2-4x=5,
等式的两边同时加上一次项系数-4的一半的平方,得
x2-4x+22=9,
配方,得
(x-2)2=9,
开方,得
x-2=±3,
解得,x1=5,x2=-1