Question

daca x+y=8 si xy=7 calculati x la a treia + y la a treia

Answer 1

$x^{3}+ y^{3}=(x+y)( x^{2} -xy+ y^{2})$
daca x+y=8⇒($(x+y)^2= x^{2} + y^{2}+2xy$
64=$x^{2} + y^{2}+2*7$
$x^{2} + y^{2}=64-14=50$
inlocuim in prima relatie
$x^{3} + y^{3}=8(50-7)$
$x^{3}+ y^{3}=8*43= 344$