Re: Cubic eqn help

From: Steve (falipey_at_gmail.com)
Date: 01/16/05 

Date: Sun, 16 Jan 2005 00:29:44 +0000 (UTC)

Thank you for your reply guys,

Todd that is a nice way of showing the assertion is true.

The question in full said this

Solve the cubic equation x^3 - 15x - 4 using the cubic formula

(refering to Cardano's formula)

Then it says from this deduce that cos(arctan(11/2)/3)= 2/sqrt(5)

I absolutely have no idea to show this

Maybe somewhere in the formula we can deduce this, but I cant see it
If someone knows how to it would be much appreciated

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