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Expand and factorise

  1. Apr 21, 2009 #1
    Can someone please help me with very simple math.. and explain slowly how they got from
    3(n+r)(n+r-1) + (n+r)
    to (n+r)(3n+3r-2)?

    I forgot how to factorise, so can someone help me do this please?
     
  2. jcsd
  3. Apr 21, 2009 #2

    CRGreathouse

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    The n+r is already factored out. Just write everything in terms of that and you'll see.

    (It's actually easier to understand by doing, in this case, than to have it explained!)
     
  4. Apr 21, 2009 #3

    Mentallic

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    Explain slowly you say? Maybe that can be expressed through example.

    ab+ac=a(b+c)
    xy+x=x(y+1)
    pqr+r=r(pq+1)

    If you understand how to do the opposite of factorising which is expanding, then these results would be easy to confirm.

    So for 3(n+r)(n+r-1) + (n+r)
    let n+r=x
    So we now have 3x(x-1)+x
    Factorising x out: x(3(x-1)+1)
    Expand 3(x-1) and collect like terms, then substitute n+r=x back into the result.
     
  5. Apr 23, 2009 #4
    Oh wow i get it now. Thank you!!
     
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