(x+1)(x+2)(x+3)(x+6)
(a+b)^2=a^2+2ab+b^2
(a+b+c)^2 = [(a+b)+c]^2 = (a+b)^2 + 2*(a+b)*c + c^2 = a^2 + 2*a*b + b^2 + (2*a + 2*b)*c = a^2 + 2*a*b + b^2 + 2*a*c + 2*b*c = a^2 + b^2 + c^2 + 2*a*b + 2*b*c + 2*a*c
(x+1)(x+2)(x+3)(x+6)+x^2
=[(x+1)(x+6)][(x+2)+(x+3)]+x^2
=(x^2+7x+6)(x^2+5x+6)+x^2
=[(x^2+5x+6)+2x])(x^2+5x+6)+...全部
(a+b)^2=a^2+2ab+b^2
(a+b+c)^2 = [(a+b)+c]^2 = (a+b)^2 + 2*(a+b)*c + c^2 = a^2 + 2*a*b + b^2 + (2*a + 2*b)*c = a^2 + 2*a*b + b^2 + 2*a*c + 2*b*c = a^2 + b^2 + c^2 + 2*a*b + 2*b*c + 2*a*c
(x+1)(x+2)(x+3)(x+6)+x^2
=[(x+1)(x+6)][(x+2)+(x+3)]+x^2
=(x^2+7x+6)(x^2+5x+6)+x^2
=[(x^2+5x+6)+2x])(x^2+5x+6)+x^2
=(x^2+5x+6)^2+2x(x^2+5x+6)+x^2
=[(x^4+25x^2+36)+2(5x^3+6x^2+30x)]+(2x^3+10x^2+12x)+x^2
=(x^4+25x^2+36+10x^3+12x^2+60x)+2x^3+10x^2+12x+x^2
=x^4+12x^3+48x^2+72x+36
。
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