初一数学题~~完全平方公式
1.(x-2)(x+2)-(x+1)(x-3)2.(ab+1)^2-(ab-1)^23.(2x-y)^2-4(x-y)(x+2y)...
1.(x-2)(x+2)-(x+1)(x-3)
2.(ab+1)^2-(ab-1)^2
3.(2x-y)^2-4(x-y)(x+2y) 展开
2.(ab+1)^2-(ab-1)^2
3.(2x-y)^2-4(x-y)(x+2y) 展开
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1.(x-2)(x+2)-(x+1)(x-3)
=(x^2-4)-(x^2-2x-3)
=2x-1
2.(ab+1)^2-(ab-1)^2
=(ab+1+ab-1)(ab+1-ab+1)
=2ab
3.(2x-y)^2-4(x-y)(x+2y)
=(4x^2-4xy+y^2)-(4x^2+4xy-8y^2)
=9y^2-8xy
=(x^2-4)-(x^2-2x-3)
=2x-1
2.(ab+1)^2-(ab-1)^2
=(ab+1+ab-1)(ab+1-ab+1)
=2ab
3.(2x-y)^2-4(x-y)(x+2y)
=(4x^2-4xy+y^2)-(4x^2+4xy-8y^2)
=9y^2-8xy
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