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    I'm having trouble with this question:

    The parametric equations of a curve are

    x = cosθ and y = 2 sinθ

    Find the equation of the normal to the curve at the point P(cosθ, 2 sinθ).

    I have found dy/dx = -2cotθ, but I do not know how to get the value of θ which I can sub in to dy/dx.

    Can someone help?

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    (Original post by lulu1997)
    I'm having trouble with this question:

    The parametric equations of a curve are

    x = cosθ and y = 2 sinθ

    Find the equation of the normal to the curve at the point P(cosθ, 2 sinθ).

    I have found dy/dx = -2cotθ, but I do not know how to get the value of θ which I can sub in to dy/dx.

    Can someone help?

    You are finding a general equation of the normal, not for a specific point
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    (Original post by lulu1997)
    I'm having trouble with this question:

    The parametric equations of a curve are

    x = cosθ and y = 2 sinθ

    Find the equation of the normal to the curve at the point P(cosθ, 2 sinθ).

    I have found dy/dx = -2cotθ, but I do not know how to get the value of θ which I can sub in to dy/dx.

    Can someone help?

    You're not meant to!

    The gradient of the tangent (and hence that of the normal) will depend on theta. Additionally, you know that the normal must pass through the given point. So your final answer will depend on theta also.
 
 
 
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