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demonstrati ca (x+1)la a 3 a -9x-9 = (x+1)(x+4)(x-2) urgent

Răspuns :

(x+1)³-9x-9=(x+1)²(x+1)=(x²+2x+1)(x+1)-9x-9=x³+2x²+x+x²+2x+1=x³+3x²+3x+1-9x-9=
x²+3x²-6x-8
in dreapta
(x+1)(x+4)(x-2)=(x²+5x+4)(x-2)=x³+5x²+4x-2x²-10x-8=x³+3x²-6x-8 deci sunt egale