问题 解答题
化简求值:
(1)[(2x2y)2-(-2xy)3-xy2(-4xy22]÷8x2y3,其中x=-1,y=-2.
(2)(m2-6mn+9n2)÷(m-3n)-(4m2-9n2)÷(2m-3n),其中m=-3,n=-
1
3
答案

(1)原式=[(4x4y2)•(-8x3y3)-xy2(16x2y4)]÷8x2y3

=[(-32x7y5)-(16x3y6)]÷8x2y3

=-4x5y2-2xy3

把x=-1,y=-2代入,原式=4×4-2×8=0;

(2)原式=(m-3n)2÷(m-3n)-(2m-3n)(2m+3n)÷(2m-3n)

=(m-3n)-(2m+3n)

=-m-6n,

把m=-3,n=-

1
3
代入,原式=3+6×
1
3
=5.

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