Ответы и объяснения

2013-04-05T12:04:19+00:00
2013-04-05T12:05:50+00:00

x^2-y^2=72   x=9-y

(9-y)^2-y^2=72

(81-18y+y^2)-y^2=72

81-18y+y^2-y^2=72

-18y+81-72=0

-18y+9=0

18y=9

y=18/9=0.5     x=8.5