Prove algebraically that the straight line with equation x = 2y + 5 is
a tangent to the circle with equation x² + y² = 5.
(2y+5)(2y+5)+y²=5
4y²+20y+25+y²=5
5y²+20y+20=0
y²+20y+100
5y²+10y+10y+20=0
5y(y+2) 10(y+2)
(5y+10)(y+2)=0
y=-2, y=-2
x=2(-2)=5
x=1
x=-1, y=2
x=-1, y=2
