poly integration

• Wireless-

  28 Apr 10, 20:54

  This qn is was asterisked. And as usual i cant do it .

   

   

  

   

   

• quailmaster

  28 Apr 10, 22:53

  try to complete the square to get a standard integration form, then refer to formula list

   

• wee_ws

  29 Apr 10, 09:46

  Hi,

    Completing the square of a quadratic function is a very helpful skill to have.

    When one encounters an expression like 1 / sqrt { f(x) }, where f(x) is a quadratic function, the result may be an inverse trigonometric (sine or cosine) or inverse hyperbolic (sine or cosine) expression.

    If one sees an expression like f'(x) / sqrt { f(x) }, the result becomes 2 sqrt { f(x) } + c instead.

    Thanks.

  Cheers,
  Wen Shih

• Wireless-

  2 May 10, 11:22

  how to complete that square.

   

  sqrt[-x^2-4x]= sqrt[-1(x^2+4x)

                      =sqrt[-1 ((x+2)^2-4) ]

   

  Then whata to do? Did i do it wrongly?

• Wireless-

  2 May 10, 11:34

  omg nvm got it. After that can jsut use the formulae. thanks!

• wee_ws

  2 May 10, 20:27

  Hi Wireless,

    You could always consider

    -x^2 - 4x = a - (x + b)^2,

    where a and b are constants to be determined.

    Thanks.

  Cheers,
  Wen Shih