 Hi and welcome to the session. Next discuss the following question. It says in figure 7.21 AC is equal to AE, AB is equal to AD and angle BAD is equal to angle EAC. Show that BC is equal to DE. So let us first understand the basic approach behind this question. We will be proving that triangle ABC and ADE are congruent is congruent to ADE. And to prove that two triangles are congruent we will be using SAS congruence criteria. So this approach is the key idea. Now we are given that AC is equal to AE and AB is equal to AD and angle BAD is equal to angle AAC and we have to prove that BC is equal to DE. So for that we will be proving that triangle ABC is congruent to triangle ADE by using SAS congruence criteria by which we need to show that two sides and the included angle of the two triangles are equal. Let us now move on to the solution. We are given that angle BAD is equal to angle EAC which implies that angle BAD plus angle DAC is equal to angle EAC plus angle DAC. This is why we are adding angle DAC to both sides which implies angle BAC is equal to angle DAE because angle BAD plus DAC is equal to angle BAC and angle EAC plus DAC is equal to angle DAE. Now in triangles ABC and ADE we have AB is equal to AD. This is given to us and angle BAC is equal to angle DAE. This we have proved above is equal to AE. This is also given to us. So we have proved that two sides and included angle of the two triangles are equal. Therefore by SAS criteria triangle ABC is congruent to triangle ADE. Now since two triangles are congruent their corresponding paths are also congruent. Hence BC is equal to DE by CPCTC that is corresponding paths of congruent triangles are congruent. Hence the result is proved. So this completes the question. Goodbye and take care.