showing the equation is true Am from writing my class test and I have failed to answer this question. None of my friends could help me after the test was over.the question reads:

If $P$ is the length of the perpendicular from the origin to the line which intercepts the axis at points $A$ and $B$, then show that $$\frac{1}{P^2}=\frac{1}{A^2}+\frac{1}{B^2}$$

Someone to help me do this.

Hint: 
Let $Q$ be the point of intersection of the lines $P$ and $AB$. Then, $\triangle AOQ$, $\triangle BOQ$, and $\triangle OAB$ are all similar. 
