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# rearranging formula watch

1. hey,
my maths teacher gave me some rearranging formula work and im stuck on two questions

1. A=4r²-Pir² make r the subject

and...

2. r-3=Pi(t-2r) make r the subject of the formula

thank you.
2. 1. Try and start by taking out a common factor on the right hand side.
2. Expand the brackets, get all the r terms on one side, then try and factorise and go from there.
3. (Original post by joshy123)
hey,
my maths teacher gave me some rearranging formula work and im stuck on two questions

1. A=4r²-Pir² make r the subject

and...

2. r-3=Pi(t-2r) make r the subject of the formula

thank you.
In both cases the crux of the matter is to expand and then collect r terms to be able to divide by the coefficient of r:
1)
2)
4. first one -

factorise out the ,

2nd one -

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Updated: February 7, 2010
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