What is the formula for the value of acceleration due to gravity at height h from the surface of the earth when h < < R ??

The value of acceleration due to gravity at height h from the surface of the earth when h < < R  is given by

$g'=g(\frac{ R}{R+h})^2=g(1+\frac{h}{R})^{-2}$

So $g'=g\left [ 1-\frac{2h}{R} \right ]$

Where

g=Value of acceleration due to gravity  at the surface of the earth