Quadratic equation related doubt

Question

How to get the formula s=1/2(αβ/α+β)t² 

Answer 1

Recommendation: state more givens, and the definitions of symbols. ALSO, PLEASE CHECK PARENTHESIZATION in order to be certain that all terms of a denominator are clustered together.

 

In other words, please improve and resubmit in the form of a question relative to definitive context.