因式分解(加50分)4x^n-13x^2y^2+9y^4xy^3+y^2+y-x+1a^2+2ab+2ac-2bc-3b
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4x^n-13x^2y^2+9y^4

=(2x-3y)^2

xy^3+y^2+y-x+1

= x(y^3-1)+y^2+y+1

= x(y-1)(y^2+y+1)+y^2+y+1

=(xy-x+1)(y^2+y+1)

a^2+2ab+2ac-2bc-3b^2

= a^2+2ab-3b^2+2ac-2bc

= (a+3b)(a-b) +2c(a-b)

=(a-b)(a+3b+2c)

(a-1)(a-3)(a-6)(a+2)+56 [常数项=-20+56=30=5*2*-3*-1]

= (a+1)(a+3)(a-2)(a-5)[之所以不取,3,1,是因为,原式有,+56不能]