Question

Can someone explain why
If R>>D then:

\left( 1- \frac{ D^2 }{ R^2 } \right)^{^1/2} approx 1-\frac{ 1 }{ 2 }\frac{ D^2 }{ R^2 }

Answer 1

\[\left( 1- \frac{ D^2 }{ R^2 } \right)^{^1/2} \approx 1-\frac{ 1 }{ 2 }\frac{ D^2 }{ R^2 }\]