



y = m x + c ---(i)
---(ii)
putting the value of y from (i) in (ii), we get
=>
here
discriminant =
=
when discriminant >0 line touches parabola at two points,
when discriminant < 0 line do not touches parabola and
when discriminant = 0 line touches parabola at one point
and we know that tangent is a line that touches the curve at exactly one point
so putting discriminat = 0 and solving
we get
on putting the value of y from line in the parabola and solving for equal roots.
If and , then
