- #1
nonequilibrium
- 1,439
- 2
Say you have a set of equations of the form
[itex]\left\{ \begin{array}{rl}
x+y+z &=a \\
xy + xz + yz &= b \\
xyz &= c
\end{array} \right. [/itex]
(for clarity: I'm working over the regular numbers)
how would you go about solving it elegantly? (or at least rewriting it as linear equations)
I'm thinking of something analogous to how you can solve
[itex]\left\{ \begin{array}{rl}
x+y &=a \\
xy &= b
\end{array} \right. [/itex]
namely by noting that (x-y)² = (x+y)² - 4xy = a² - 4b (and after taking the square root we're left with two good ol' linear equations, i.e. x+y=... and x-y=..., a form which I regard as "being solved")
[itex]\left\{ \begin{array}{rl}
x+y+z &=a \\
xy + xz + yz &= b \\
xyz &= c
\end{array} \right. [/itex]
(for clarity: I'm working over the regular numbers)
how would you go about solving it elegantly? (or at least rewriting it as linear equations)
I'm thinking of something analogous to how you can solve
[itex]\left\{ \begin{array}{rl}
x+y &=a \\
xy &= b
\end{array} \right. [/itex]
namely by noting that (x-y)² = (x+y)² - 4xy = a² - 4b (and after taking the square root we're left with two good ol' linear equations, i.e. x+y=... and x-y=..., a form which I regard as "being solved")