Question

calculate the focal length of concave mirror by us method​

Answer 1

Answer:

Your question is confusing me

Answer 2

Question:

Calculate the focal length of concave mirror by using method.

Answer:

Use the below formula,

$\bold{\dfrac{1}{f} = \dfrac{1}{u} +\dfrac{ 1}{v}}$

(don't forgot to apply sign convention)