Ответы и объяснения

2013-07-24T19:22:13+00:00
    x2-xy-y2 =19         
    x-y=7

(x-y)(x+y)-xy=19
7(x+y)-xy=19
x(7-y)=19-7y
x=(19-7y)/(7-y)

x(x-y)-y2=19
7x-y2=19
x=(19+y2)/7


(19+y2)/7 == (19-7y)/(7-y)

133-49y=133+7y2-19y-y3
y3-7y2-30y=0
y(y2-7y-30)=0
y1=0
y2-7y-30=0    D=49+120=169

y1=(7+13)/2=10
y2=(7-13)/2=-3

ПОтом найдем x :  x1=7+y=7+10=17
                               x2=7-3=4  

2013-07-24T20:37:24+00:00