How many images of an object will be formed when it is placed in front of two mirrors at an angle of 72 with each other?

Question 8 Exercise 7B

Answer:

(a) The number of images formed when an object is placed between the two plane mirrors at an angle of 90°, is 3. Three images are formed.

We know that two mirrors kept perpendicular to each other, produce three images for an object that is placed in between them.

i.e, the angle between two mirrors is 60°, n=360°/90° = 4, number of images = n-1 = 4-1 = 3.

(b) The number of images formed if an object is placed between two plane mirrors with an angle of 60°, is five. Five images are formed:

i.e, the angle between two mirrors is 60°, n=360°/60° = 6, number of images = n-1 = 6-1 = 5.

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I'm a little confused here since there are varying answers on the internet, and I cannot find any legitimate sources explaining this problem.

According to what I've seen, the formula is simply $$ N = \frac{360^\circ}{A} - 1 $$ However, other sources say that $N$ needs to be an odd number (I do not know why), so when $N$ is even, the answer is actually $N+1$.

If I used the first method, then the answer would be $N=\dfrac{360^\circ}{72^\circ}-1=4$. If I followed the second method, then the answer would be $N+1=5$. (I have actually found some people saying it's 4 and others saying it's 5.)

Could anyone clarify this for me?