We have to find out the force which is being exerted by the four charges on the corners of a pentagon. This is a pentagon having five points. There are four plus q charges at the four points and the fifth one there is nothing. We have to find the force at the center which is equidistant from all these sides. So, in case of pentagon these angles by the virtue of symmetry are equal and each of this angle is 72 degree. These angles are 72 degree. Now, this problem requires some imagination. We will presume that there is a charge here also. Just a presumption. Let us see how it simplifies the problem. Otherwise, it becomes very clumsy. Now, let there be charge at all the five points. Each one is exerting a similar electric field and let there be a plus q charge at this point. We have to find out the force exerted at the point which is a charge which is at the center. And we are given that all these distances are given as A. Now, by symmetry we can say the force exerted by each pair means this force exerted on q here due to this one, this one, this one, this one, this one all are equal in magnitude but not in direction. Force the magnitude of force by each will be q square upon 4 pi e 0 A square. Let me write this as F. Small F I will write. And now draw the diagram for finding out the resultant force due to these 1, 2, 3, 4, 5. By guesswork, we can say it should be 0 by symmetry but in physics, we should not go by guess simply by guesswork. We should show it analytically. Now, draw this force first. Take anyone. Let us draw this one first. This is the direction and let this be the magnitude. This is F. F1, magnitude of all are equal. Now, take this one. This is making 72 degree here but the direction is like this. So, it is like this. Now, take this one. It is making 72 degree with this one and the 72 degree of this one will come like this. It is 72 degree here. This is 72 degree. This is 72 degree. Now, we have drawn 3. Take the other one. We have taken this. This and this. Take this one. It makes 72 degree with this like this. So, it will be somewhat like this. Angles are just approximation because I am not using compass and all. So, I am drawing by free hand. So, this will be another F. Now, we come to the last one. This one. This is making 72 degree with it. So, 72 degree with it. If you draw it using compass and all measurement, you will find this will close. This will close and it will be again in the shape of pentagon. And what happens in such cases, the resultant force is 0 of all the 5 charges. So, force because of the 5 charges is 0 because this is the closed loop which we are getting of all the forces acting on the system, which is q here. Now, we have taken 5 charges which are not there. This charge was not there but we have taken. The force due to 5 is 0. If we remove this charge, the force is not 0. Force is not 0. There will be some force because of 1, 2, 3, 4. Force, this let that be F dash. Let that be F dash. The resultant of this, this, this, this is F dash. If we again place q here, this will be 0. It means the force exerted by this is equal in magnitude to this and opposite in the direction. So, the magnitude of force exerted by 1 charge would be equal to the resultant magnitude of the 4 charges. I will again repeat so that it is easier to understand. We had assumed that there are 5 charges. With that, we have come to know that with 5 charges, the resultant force is 0. Now, remove the 5th charge. When you remove the 5th charge, you know the resultant will not be 0. It will be something. If you place this 5th charge again, resultant has to be 0 and how that will be 0? It will be 0 when the magnitude of this force is equal to this force and opposite in the direction. So, the magnitude of F dash is F. So, the force exerted by the 4 charges is this. It is equal to the force had there been only 1 charge is equal to this. So, this is the answer to the problem. You can do similar problem in case of hexagon also in case it is given. So, that is all on it. Thank you.