Core 4: Parametric Equations, Help with exam question! Watch

Jonsmith98
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Hi everyone!

So I am just reviewing a past paper that I have done and am having trouble understanding the solution to a question.

For reference the question is 4(b) on the AQA Core 4 January 2013 Paper.

Question:
http://filestore.aqa.org.uk/subjects...N13.PDF#page=8
Answer:
http://filestore.aqa.org.uk/subjects...N13.PDF#page=8

So my issue is that I do not understand why when each of the parametric equations are square, 4 and -4 are introduced into the equations, my understanding was that then 2/t was squared it results in 4/t2 and when t was squared it simply results in t2. Im not sure if my question is clear or not so if any further clarification is needed please ask!

Thanks for any help and support!
Oh and have a happy NUT strike day tomorrow!
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nerak99
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I think that maybe you are just forgetting the cross terms in the multiplication of the brackets.

e.g. -2ab in this expansion. (a-b)^2=a^2-2ab+b^2
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Zacken
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(Original post by Jonsmith98)
Hi everyone!
Do you know how to expand brackets of the form (a+b)^2? If not - this is how: (a+b)^2 = (a+b)(a+b) = a(a+b) + b(a+b) = a^2 + ab + ab + b^2 = a^2 + 2ab + b^2

In this case, for x, for example, we have:

\displaystyle \left(t + \frac{2}{t}\right)^2 = t^2 + 2 \times t \times \frac{2}{t} + \left(\frac{2}{t}\right)^2

And 2 \times t \times \frac{2}{t} = \frac{4t}{t} = 4.

Can you do the same for y?
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Jonsmith98
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(Original post by nerak99)
I think that maybe you are just forgetting the cross terms in the multiplication of the brackets.

e.g. -2ab in this expansion. (a-b)^2=a^2-2ab+b^2
(Original post by Zacken)
Do you know how to expand brackets of the form (a+b)^2?
*Face hits desk*
Thanks guys for the help, I had a feeling it was something frustratingly obvious. I think its just a new format that im not used to that caught me out.
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