化简
(-x^3-3x^2+7x-8)-(-3x^3-2x^2-5x+4)-(-x^3-2x^2+2)
求值
1.已知A=2a^3-4b^2 B=3b^2+a^3 求2A-B
2.如果一个长方形的一边为a+b,另一边为a-b，试求这个长方形的周长.
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參考答案:原式=-x^3-3x^2-7x-8+3x^3+2x^2+5x-4+x^3+2x^2-2
=3x^3+x^2+12x-14
因为A=2a^3-4b^2 B=3b^2+a^3
所以2A-B=2（2a^3-4b^2）-（3b^2+a^3）
=4a^3-8b^2-3b^2-a^3
=3a^3-11b^2
2[(a+b)+(a-b)]
=2[2a]
=4a
