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# Core 4 Parametric Equations Watch

1. Hello,

I was wondering if anyone would be kind enough to help me. It's question 10 I need help with.

I'm struggling with part a where dy/dx = 6cost (I know it's actually theta, but I will abbreviate to 't' for convenience).

When I differentiate x and y, I get:

dx/dt = -2sint

dy/dt = -6sin2t

and as dy/dx = (dy/dt)/(dx/dt), I get -6sin2t/-2sint, but I don't see how this makes 6cost. Could anyone point me in the right direction?

Thank you.
Attached Images

2. use double angle formula for sine.

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