# Roots of Cubic

• Nov 25th 2012, 01:15 PM
minicooper58
Roots of Cubic
Hi , I don't know what's going on here with the sigma notation (attached question and answer) .
A simplified explanation would be greatly appreciated .

Thank you
• Nov 25th 2012, 01:22 PM
coolge
Re: Roots of Cubic
There are a many sigmas/ Which one are you referring to?
• Nov 25th 2012, 01:25 PM
minicooper58
Re: Roots of Cubic
Hi , alpha=2 the first one and then why gamma is omitted in the second .
• Nov 25th 2012, 01:37 PM
Plato
Re: Roots of Cubic
Quote:

Originally Posted by minicooper58
Hi , I don't know what's going on here with the sigma notation (attached question and answer) .
A simplified explanation would be greatly appreciated .

The cubic is $z^3-2z^2+0z+k=0$

The sum of the roots; $\alpha+\beta+\gamma=2$

The product of roots two at a time: $\alpha\beta+\alpha\gamma+\beta\gamma=0$

The products of the roots: $\alpha\beta\gamma=-k$