Cauchy-Schwarz is pretty helpful
Algebra
Level
2
Let \(a\), \(b\), \(c\) and \(d\) be positive reals such that \(a + b + c + d = 1\). Find the minimum value of \(\dfrac {1}{a} + \dfrac {1}{b} + \dfrac {1}{c} + \dfrac {1}{d}\).
by
Sharky Kesa