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# C4 question watch

1. x=2cos(theta) + sin (theta)
y= cos (theta) + 2sin (theta)

Show that for any point on the curve x^2 + y^2 = 5 + 4sin2(theta).
I tried squaring both x and y and adding them together but I cant seem to get the right answer.
2. (Original post by Fross877)
x=2cos(theta) + sin (theta)
y= cos (theta) + 2sin (theta)

Show that for any point on the curve x^2 + y^2 = 5 + 4sin2(theta).
I tried squaring both x and y and adding them together but I cant seem to get the right answer.
Correct approach.

Let's see what you've written to determine where you're tripping up.
3. (Original post by RDKGames)
Correct approach.

Let's see what you've written to determine where you're tripping up.
x^2 + y^2 = 5cos^2 (theta) + 3sin^2 (theta)
4. (Original post by Fross877)
x^2 + y^2 = 5cos^2 (theta) + 3sin^2 (theta)
OK, that's not much to go on, it is clearly wrong.

How did you get to this point? Show your working out.
5. (Original post by RDKGames)
OK, that's not much to go on, it is clearly wrong.

How did you get to this point? Show your working out.
6. (Original post by Fross877)
...
GCSE type mistake.

Expand the brackets and you'll notice that it is not just
7. (Original post by Fross877)
You've squared x and y wrong - remember to multiply each term by each term.

i.e. (a+b)^2 = a^2 + 2ab + b^2, not just a^2 + b^2

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