"All limits, especially national ones, are contrary to the nature of mathematics… Mathematics knows no races… For mathematics the whole cultural world is a single country" – David Hilbert, the foremost mathematician of the 20th century, speaking as the Nazis neared power in his native Germany.
Solving cubics and quartics – video clips
First watch this video (not mine) about sums and products of roots with quadratics:
Then work through this video of mine.
Work through the three examples I do, one by one, pausing after each one.