Greeings,

The equation below is given and the problem is to find all values of m, for which the roots of the equation form an arithmetic progression.

Though, I am pretty sure Vieta's formulae are to be used, I am puzzled by the fact they are usable in quadratic equations only..

I've considered a substitution of the x^2=y like, but then I loose the link between the substituted equation's roots and the biquadratic equation's roots..

Thank you.