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#1 2007-05-10 05:08:55

Birdie
Guest

sats question

Hi i'm a noob here i just need an answer to this question thats been killing me. it came up on the year 9 SATs (ks3) i have a number i square it and -25. With the same number i -25 then square it for both equations i get the same answer. What was my original number.
I think it looks like this (X-25)2 = x2-25

#2 2007-05-10 05:14:46

Huddy
Guest

Re: sats question

Hi i also got that question because i did the 6-8 paper, its one of the level 8 questions that also baffled me, none of the people who did 5-7 knew it, as the question doesn't crop up in their paper.

#3 2007-05-10 05:33:39

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: sats question

You have this equation:
(x-25)² = x² - 25

First you need to expand the brackets on the left side:
x² - 50x + 625 = x² - 25

Then simplify:
50x = 650

And solve:
x = 13.

That's a surprisingly mean question for KS3 SATs though.
I was helping my cousin revise for them last weekend, and nothing that bad came up.


Why did the vector cross the road?
It wanted to be normal.

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#4 2007-05-10 05:50:40

Birdie
Guest

Re: sats question

Ahhhh yes thank you very much for putting my brain to rest. Its all simple when you know the answer. Ta very much for the effort i will impress my teacher tomorrow.

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