Question

how many no of images will be formed if 2 plane mirrors were inclided at the angle of 180°

Answer 1

$n = \frac{360}{a} - 1$

$n = \frac{360}{180} - 1$
$n = 2 - 1 \\ n = 1$
Therefore, one image will be formed.
Here, n=> No. of images
a=> Angle formed.

Answer 2

n=360/o -1
n=360/180-1
n=2-1=1
no of images =1