question: kiedy tau ryczy?
answer: \begialign} \operatorname{tri}(t) = \operatornamrect}(t) \operatorname{rect}(t) \quad &\overse\underset{\mathrdef}}{}=} \int_{-\infty}^\infty \mathrrect}(\tau) \cdot \mathrm{rect}(t-\tau)\ d\tau\\ &= \int-\infty}^\infty \mathrm{rect}(\tau) \cdot \mathrrect}(\tau-t)\ d\tau .