题目内容
已知方程组
,用简便方法求7x(x-3y)2-2(3y-x)3的值.
|
解方程组
得:
,
7x(x-3y)2-2(3y-x)3
=7x(x-3y)2+2(x-3y)3
=(x-3y)2[7x+2(x-3y)]
=(x-3y)2(9x-6y)
=3(x-3y)2(3x-2y)
原式=3×12×(3×
-2×
)
=3×
=
.
|
|
7x(x-3y)2-2(3y-x)3
=7x(x-3y)2+2(x-3y)3
=(x-3y)2[7x+2(x-3y)]
=(x-3y)2(9x-6y)
=3(x-3y)2(3x-2y)
原式=3×12×(3×
5 |
2 |
1 |
2 |
=3×
13 |
2 |
=
39 |
2 |
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