* Developing a system of algebraic notation: He introduced the use of letters to represent unknown quantities, which was a major step forward in the development of algebra.
* Solving equations using radicals: He made significant contributions to the solution of equations, including the development of methods for solving cubic and quartic equations.
* Developing the Viète's formulas: These formulas relate the coefficients of a polynomial to the sums and products of its roots.
So, when you see "Vieta," it likely refers to François Viète, the mathematician, or to some concept or theorem related to his work.
To be sure, you'll need to provide more context! What are you reading or talking about that includes the word "Vieta"?