If x=C(m,2) then m in terms of x ???

Question

Sir it is from permutation and combination

Answer 1

 C(m,2) = m! / [(2!)(m-2)!]

 

            = m(m-1)/2

 

So, 2x = m(m-1)

 

     m² - m - 2x = 0

 

Using the quadratic formula, m = [1±√(1+ 8x)] / 2