How to prove this convolution problem?

[clw]

Homework Statement

How do I prove that sinc(t) * sinc(t) = sinc(t)?

Homework Equations

The Attempt at a Solution

I converted it to frequency domain and got that rect(f) rect (f) = rect (f) which then converts back to sinc (t). But I'm just curious as how would I go about doing this if I don't convert to frequency domain? I get

$\int ^{\infty} _{-\infty} sinc(\tau) sinc( t- \tau) dt$

I get stuck at this integral. Any help would be very much appreciated!

 

[rude man]

Tall order, I think.