Toán Lớp 8: Thực hiện phép tính: a, (x+2)(1+x-x^2+x^3-x^4)-(1-x)(1+x+x^2+x^3+x^4) b, (2b^2-2-5b+6b^3)(3+3b^2-b) c, (4a-4a^4+2a^7)(6a^2-12-3a^3)

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1. a)(x+2)(1+x-x^2+x^3-x^4)-(1-x)(1+x+x^2+x^3+x^4)

   =x+x^2-x^3+x^4-x^5+2+2x-2x^2+2x^3-2x^4-1-x-x^2-x^3-x^4+x+x^2+x^3+x^4+x^5

   =(x+2x-x+x)+(x^2-2x^2-x^2+x^2)+(-x^3+2x^3-x^3+x^3)+(x^4-2x^4-x^4+x^4)+(-x^5+x^5)

   =3x-x^2+x^3-x^4

   b)(2b^2-2-5b+6b^3)(3+3b^2-b)

   =6b^2-6-15b+18b^3+6b^4-6b^2-15b^3+18b^5-2b^3+2b+5b^2-6b^4

   =18b^5+(6b^4-6b^4)+(18b^3-15b^3-2b^3)+(6b^2-6b^2+5b^2)+(-15b+2b)-6

   =18b^5+b^3+5b^2-13b-6

   c)(4a-4a^4+2a^7)(6a^2-12-3a^3)

   =24a^3-48a-12a^3-25a^6+48a^4+12a^7+12a^9-24a^7-6a^10

   =-6a^10+12a^9+(12a^7-24a^7)-25a^6+48a^4+(24a^3-12a^3)-48a

   =-6a^10+12a^9-12a^7-25a^6+48a^4-12a^3-48a

   $\text{@ThanhTruc2008}$

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