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# FP1 Matrices Question watch

1. I managed to do part A and I attempted part B but I can't tell where I went wrong with it:

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2. (Original post by creativebuzz)
I managed to do part A and I attempted part B but I can't tell where I went wrong with it:

So you have det(P)=2P^2 - P

Then use the formula : area of image = area of object x det(P)
3. (Original post by stardude8)
So you have det(P)=2P^2 - P

Then use the formula : area of image = area of object x det(P)
Oh okay!

So where did I go wrong here:

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4. (Original post by creativebuzz)
Oh okay!

So where did I go wrong here:

det (p) does not equal 1/(2p^2 - p) , but simply 2p^2 - p. You only use the reciprocal when finding the inverse matrix, which you are not doing here.
5. (Original post by stardude8)
det (p) does not equal 1/(2p^2 - p) , but simply 2p^2 - p. You only use the reciprocal when finding the inverse matrix, which you are not doing here.
Ah thank you! (Positive rating for being such a help )!

Would you mind helping me on this question?

I managed to get the 'show' part of the question, but this is as far as I got for the second part of the question!
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6. (Original post by creativebuzz)
Ah thank you! (Positive rating for being such a help )!

Would you mind helping me on this question?

I managed to get the 'show' part of the question, but this is as far as I got for the second part of the question!
First make sure you're using the correct line equation from the question - the last t should be squared.

So you know the general equation of a circle is (x-a)^2 +(y-b)^2 = r^2 . Substitute in your 3 coordinates into these equation, and as the radius is always the same, you can set two of the equations to be equal to one another.
E.g. with
(0,0) (0,at)
(0-a)^2 +(0-b)^2 =a^2 +b^2 =r^2
(0-a)^2 +(at-b)^2=a^2 + (at)^2 -2atb+b^2=r^2

They both equal r^2, so put them together and solve for b. Do the same with another two coordinates to find a

N.B. (a,b) would then be the centre of the circle.
7. You got really neat handwriting. #Jealous
8. (Original post by Tiri)
You got really neat handwriting. #Jealous
Ahah, that's actually my handwriting when I'm rushing but thank you #appreciative

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