A.计算:1.(a+b)(a-2b)-2(a+2b)(a-b)===2.5x(X^2+2X+1)-(2x+3)(x-5)===

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A.计算:1.(a+b)(a-2b)-2(a+2b)(a-b)===2.5x(X^2+2X+1)-(2x+3)(x-5)===
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A.计算:1.(a+b)(a-2b)-2(a+2b)(a-b)===2.5x(X^2+2X+1)-(2x+3)(x-5)===
A.计算:
1.(a+b)(a-2b)-2(a+2b)(a-b)
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2.5x(X^2+2X+1)-(2x+3)(x-5)
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A.计算:1.(a+b)(a-2b)-2(a+2b)(a-b)===2.5x(X^2+2X+1)-(2x+3)(x-5)===
1.(a+b)(a-2b)-2(a+2b)(a-b)
=(a^2-2ab+ab-2b^2)-2(a^2-ab+2ab-2b^2)
=(a^2-ab-2b^2)-(2a^2+ab-4b^2)
=-a^2-2ab+2b^2
2.5x(X^2+2X+1)-(2x+3)(x-5)
=(5x^3+10x^2+5x)-(2x^2-10x+3x-15)
=5x^3+8x^2+12x+15