Solution:
Any point on the parabola is .
Now tangent at is
If it is a tangent to the parabola, , then
Since it has equal roots, so
,
Hence, the equation of the common tangent is , .
The equation of the common tangent to the parabola and is /are
Any point on the parabola is .
Now tangent at is
If it is a tangent to the parabola, , then
Since it has equal roots, so
,
Hence, the equation of the common tangent is , .