http://www.osce.org/docs/english/1990-1999/summits/helfa75e.htm
This was signed by 35 nations Organization for Security and Co-operation in Europe in Helsinki in 1975.
... quadratic formula expresses the explicit solution(s) x to the quadratic equation <math>ax^2+bx+c=0</math> in terms of the coefficients a, b and c, ...