>.< need help on maths

• mystiv

  27 Sep 05, 00:26

  cham. too long never do liao. simple sum also dunnoe. help guys?
  
  'Factorise completely c^2 - 9a^2 - b^2 +6ab'
  
  
• the Bear

  27 Sep 05, 00:32

  9a^2 - 6ab + b^2 = (3a - b)^2
  
  then c^2 - (3a - b)^2
  = (c - (3a - b))(c + (3a - b))
  = (c + b - 3a)(c - b + 3a)
  
  i think
  
  

  Originally posted by mystiv:

  cham. too long never do liao. simple sum also dunnoe. help guys?
  
  'Factorise completely c^2 - 9a^2 - b^2 +6ab'
  
  

• mystiv

  27 Sep 05, 00:34

  Originally posted by the Bear:

  9a^2 - 6ab + b^2 = (3a - b)^2
  
  then c^2 - (3a - b)^2
  = (c - (3a - b))(c + (3a - b))
  = (c + b - 3a)(c - b + 3a)
  
  i think
  
  

  pro