## solving a cubic equation

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### solving a cubic equation

take a look at this:
http://www.wolframalpha.com/input/?i=so ... 2%2Bcx%2Bd

soo... can somebody tell me what happened, or where I can find an explaination for the first 3 equations
Q.E.D. , or not?
Zapp
University

Posts: 124
Joined: Thu Feb 10, 2011 3:49 pm

### Re: solving a cubic equation

Wikipedia has an article on it. As I recall (dimly), the basic way to solve the equation is

(1) reduce the x-squared term by using x = t - (b/3a). This leaves us with an equation of the form t^3 + pt + q = 0

(2) let t = u + v, and add another condition that 3uv + p = 0. This allows us to find two roots of our new equation, u^3 and v^3.

(3) work back to find the third root, and then back again to get the roots for the original quadratic equation.

It always seemed like more trouble than it was worth to me--it was enough to know it was possible.
bmonk
University

Posts: 133
Joined: Thu Feb 10, 2011 4:03 pm

### Re: solving a cubic equation

Oddly enough, one of the people that I read regularly rather recently addressed this question (in two parts):

Part 1
Part 2

xander

xander
University

Posts: 154
Joined: Fri Feb 11, 2011 12:14 am
Location: Sparks, NV, USA

### Re: solving a cubic equation

thanks! helped me a lot.
Q.E.D. , or not?
Zapp
University

Posts: 124
Joined: Thu Feb 10, 2011 3:49 pm