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Sa se arate ca:

[tex][( \frac{a+1}{a-1})^3-1+3* \frac{a+1}{a-1}-3*( \frac{a+1}{a-1})^2]:[3( \frac{a-1}{a+1})^2-( \frac{a-1}{a+1})^3-3( \frac{a-1}{a+1})+1] [/tex] [tex]= (\frac{a+1}{a-1})^3 [/tex]


Răspuns :

Notam x=(a+1)/(a-1) si y=(a-1)/(a+1).

Deci expresia din enunt este egala cu (x^3-1+3x-3x^2)/(3y^2-y^3-3y+1)=(x-1)^3/(1-y)^3=[(x-1)/(1-y)]^3.

x-1=2/(a-1)
1-y=2/(a+1)

Deci [(x-1)/(1-y)]=[(2/(a-1))/(2/(a+1))]^3=[(a+1)/(a-1)]^3.