Math problem

Hay guys how do I solve for this? a,b,c,d are constants and I have to solve for v,x,y,z.

v (x + y + z) = a
x (v + y + z) = b
y (v + x + z) = c
z (v + x + y) = d

Okay I tried working it out and eventually got to

a = v/2 { 3(a+v) +- sqrt[(a+v)^2 - 4b] +- sqrt[(a+v)^2 - 4c] +- sqrt[(a+v)^2 - 4d] }

How do I solved for v? I am pretty sure this is the wrong way to do it though...

>>2
That makes it so you have 6 variables (m = xy, n = vy and so on) but only 4 equations.