Talk:Parametric resonance

Is the equation correct?

I'm not familiar with this area of physics/maths but surely the equation given in the article, $ii+(a+B\cos t)u=0\$ is not correct? Is $ii$ supposed to be ${\ddot {u}}$ or something else? There's no explaination of what 'i' is and if i is something, why isn't it written as $i^{2}$? AlphaNumeric 11:56, 21 October 2007 (UTC)