27.c x⁴+1/x⁴=[(x²+(1/x)²-√2x*1/x][x²+(1/x)²+√2x*(1/x)]=
ridicand la patrat relatia x+1/x=2 rezulta x²+1/x²=2
(2-√2)*(2+√2)=4-2=2
28.a ridicam la patrat x-1/x=3⇒x²+1/x²=11
b ridicam la puterea a treia x³-3x*1/x+3x*1/x²-1/x³=27
⇒x³-1/x³=27-3(x-1/x)=27-3*3=27-9=18
⇒x³-1/x³=18
28.c aplicam a⁴+b⁴=(a²+b²-√2*ab)(a²+b²+√2ab)
as putea rezolva tot,dar te rog,incearca si tu.Daca le prinzi gustul sa vezi ce usoare sunt
succes!
29, cunoastem x+y=4 x*y=3
a)(x+y)²=4²=16
b) x²+y²=(x+y)²-2xy=4²-2*3=10
c)(x-y)²=x²-2xy+y²=10-6=4
d1/x+1/y=(x+y)/xy=4/3
