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This has been bugging me all day. It seems like a very straight forward question but for whatever reason, I just cannot get my answer in the right format.

The question reads -

The parametric equations of a curve are

x = sin(2A) + 2sin(A)

y = cos(2A) - 2cos(A), where 0 < A < PI

Show that dy/dx = -(sinA) / (1 + cosA)

The differentiation is fine, I can do that without problems and I checked WolframAlpha to make sure I was correct in that but I just cannot simplify the dy/dx to the required format whatever I do. I keep getting very close in the different ways but never exactly what I need. I would be very grateful if someone could help.

Tip: You need to find dx/dA and dy/dA first then invert dx/dA and multiply them together to get to dy/dx

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    The piece you're likely missing is the double-angle formulas for sin and cos; you should try expanding out sin(2A) and cos(2A) and see if that makes any difference?2011-05-20
  • 0
    You can use the chain rule $dy/dA=(dy/dx)(dx/dA)$ and solve for $dy/dx$.2011-05-20

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