I am confusing... - intercept form

" vertex form lecture"
Hi. At the beginning of the video that was said:

We have now seen a useful way to write a formula to quickly find the roots of our equation

But in the examples we solved, we already had the roots of our parabola…
(In Intercept-Form, we had p and q before solving equation…)
What does that mean?!
for example consider this one from intercept challenge:

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