Maths > Parabola > 8.0 Equation of tangent to a parabola

  Parabola
    1.0 Conic Section
    2.0 Parabola
    3.0 Standard equation of Parabola
    4.0 Focal distance of a point
    5.0 General equation of Parabola
    6.0 The generalized form of parabola: ${\left( {y - k} \right)^2} = 4a\left( {x - h} \right)$
    7.0 Parametric Co-ordinates
    8.0 Equation of tangent to a parabola
    9.0 Point of intersection of tangents at any two points on the parabola
    10.0 Equation of normal to the parabola
    11.0 Relation between parametric coefficients if normal meets parabola
    12.0 Important relations
    13.0 Circle through co-normal points
    14.0 Chord of contact

8.3 Parametric form
As we know that the equation of tangent to parabola ${y^2} = 4ax$ at a point $({x_1},{y_1})$ using $T=0$ is $$y{y_1} = 2a\left( {x + {x_1}} \right)$$
To find the equation of tangent to the parabola ${y^2} = 4ax$ at the point $P(a{t^2},2at)$, put ${x_1} = a{t^2}$ and ${y_1} = 2at$, we get $$y\left( {2at} \right) = 2a\left( {x + a{t^2}} \right)$$ $$yt = x + a{t^2}$$
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