X+y-7=0 x=7-y
x²+yx+y²=43 (7-y)²+(7-y)y+y²-43=0 y²-14y+49+7y-y²+y²-43=0
y²-7y+6=0 y1=(7-√(49-24))/2=1 y2=6
x1= 6 x2=1
x+y=3 x=3-y
x²-y²-4yx+11=0 (3-y)²-y²-4y(3-y)+11=0 y²-6y+9-y²-12y+4y²+11=0
4y²-18y+20=0 ⇔ 2y²-9y+10=0
y1= (9-√(81-80) )/4=2 y2=5
x1=3-2=1 x2= 3-5=-2