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1. I'm stuck on a question from the C4 book (chapter 6, Mixed Exercises 15 (d)).

I understand finding the area of the whole triangle, but not how to find the area of A1. Why is the curve 4sinθ(-5sinθ)? I know how to go from there, but not how they got that equation.

Thanks guys!
2. (Original post by кяя)
I understand finding the area of the whole triangle, but not how to find the area of A1. Why is the curve 4sinθ(-5sinθ)? I know how to go from there, but not how they got that equation.

Thanks guys!

3. (Original post by кяя)
...
As an alternative to the above (I prefer this once since you get used to the idea of substitutions being scalings and this will help once you do multivariate calculus and need to deal with Jacobians, but I digress):

You know the area under a curve is given in cartesian co-ordinates as , yes? But at the same time you can think of since they 's kind of cancel.

Let's go ahead and re-write this now:

Now you know that and and but then the negative sign means you flip them, so you're left with:

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