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| $(1/3x^2+1)^3+8/3x^3=(1/3x^2-1)^3+2/3(x+1)^4$ | di Francesca Ricci |
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$(1/3x^2+1)^3+8/3x^3=(1/3x^2-1)^3+2/3(x+1)^4$ Il cubo del binomio si calcola svolgendo il cubo del primo $(a+b)^3=a^3+b^3+3a^2b+3ab^2$ Scomponiamo $(x+1)^4$ come $(x+1)^2*(x+1)^2$: $(1/3x^2)^3+1^3+3(1/3x^2)^2*1+3*1/3x^2*1^2+8/3x^3=(1/3x^2)^3+(-1)^3+3(1/3x^2)^2*(-1)+3*1/3x^2*(-1)^2+2/3*(x+1)^2*(x+1)^2$ $1/27x^6+1+x^2+1/3x^4+8/3x^3=1/27x^6-1+x^2-1/3x^4+2/3*(x^2+1+2x)*(x^2+1+2x)$ $1/27x^6+1+x^2+1/3x^4+8/3x^3=1/27x^6-1+x^2-1/3x^4+2/3*(x^4+x^2+2x^3+x^2+2x+1+2x^3+2x+4x^2)$ $1/27x^6+1+x^2+1/3x^4+8/3x^3=1/27x^6-1+x^2-1/3x^4+2/3x^4+2/3x^2+4/3x^3+2/3x^2+4/3x+2/3+4/3x^3+4/3x+3/8x^2$ Trasportiamo tutti i termini al primo membro e semplifichiamo: $1/27x^6+1+x^2+1/3x^4+8/3x^3-1/27x^6+1-x^2+1/3x^4-2/3x^4-2/3x^2-4/3x^3-2/3x^2-4/3x-2/3-4/3x^3-4/3x-3/8x^2=0$ $-12x^2-8x+4=0$ $12x^2+8x-4=0$ Svolgiamo l'equazione trinomia completa: $x=(-8\pm\sqrt(64+192))/24=(-8\pm\16)/24=$ $(-8+16)/24=8/24=1/3$ $(-8-16)/24=-24/24=-1$
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