Question

calculati x+y+z stiind ca x,y,z apartine R si x²+y²+z²=216 si xy-yz+zx=230

Answer 1

(x+y+z)² = x²+y²+z² + 2*(xy+xz+yz)  inlocuin valorile cunoscute ...
(x+y+z) = √(216+2*230)=
             = √676 = ...  + 26 sau -26

Answer 2

(x+y+z)²=x²+y²+z²+2(xy+yz+zx)
(x+y+z)²=216+2*230
(x+y+z)²=216+460=676
x+y+z=+-√676
x+y+z=+-26
S={-26;26}