Répondre :
Si on a (x+1/x)^2=7 alors x^3+1/x^3=?
x+1/x=rac(7)=7^(-0,5)
(x+1/x)^3=x^3+3*x^2*1/x+3*x*1/x^2+1/x^3
(7^(-0,5))^3=x^3+1/x^3+3*(x+1/x)
x^3+1/x^3=7^(-1,5)-3*7^(-0,5)
=1/(7rac(7))-3/rac(7)
=(-20)/(7*rac(7))
x+1/x=rac(7)=7^(-0,5)
(x+1/x)^3=x^3+3*x^2*1/x+3*x*1/x^2+1/x^3
(7^(-0,5))^3=x^3+1/x^3+3*(x+1/x)
x^3+1/x^3=7^(-1,5)-3*7^(-0,5)
=1/(7rac(7))-3/rac(7)
=(-20)/(7*rac(7))