:=+=-:=-1oo
7
xx
1o
5
43784o
25155
3
56
x+y=6xy=7x2+y2
x+y=6x+y2=36x2+y2+2xy=36xy=72xy=14x2+y2=36-14=22
:x18o-x9o-x9o-x3=18o-xx=4545
6
4