280

ե) {x-y=11

∑xy=12

{x=11+y

{y(11+y)=12

11y+y^2=12

y^2+11y+12=0

D=121+48=169=13^2

y1=13+11/2=12 y1=12

y2=13-11/2=1 y2=1

{y1=1

{x=11+1=12

{y2=12

{x=-11-1=-12

283

զ) {x^2+y^2+z^2=35

{x+y=2

{x-z=4

{x^2+y^2+z^2=35

{y=2-x

{z=4-x

x^2+(2-x)^2+(4-x)^2=35

x^2+4-4x+x^2+16-8x+x^2=35

3x^2-12x-15=0 /:3

x^2-4x-5=0

D=16+20=36=6^2

x1=4+6/2=5

x2=4-6/2=-1

{x=5, y=-3

{x=-1, y=3

{z=-1, x=5

z=5, x=-1