由①得
x=1+2y ③
③代入②
(1+2y)²+y²=25
4y²+4y+1+y²=25
5y²+4y-24=0
y1=(-2+2√31)/5 y2=(-2-2√31)/5
x1=1+2y1=(1+4√31)/5 x2=1+2y2=(1-4√31)/5
解方程组x-2y=1 ① x²+y²=25 ②
由①得
x=1+2y ③
③代入②
(1+2y)²+y²=25
4y²+4y+1+y²=25
5y²+4y-24=0
y1=(-2+2√31)/5 y2=(-2-2√31)/5
x1=1+2y1=(1+4√31)/5 x2=1+2y2=(1-4√31)/5