 Hi, and welcome to the session. Let us discuss the following question. The question says, find the sum to indicate the number of terms in each of the geometric progressions in exercises 7 to 10. Given geometric progression is 1 minus a a squared minus a cubed, so on up to n terms, if a is not equal to minus 1. Before solving this question, we should know that sum of n terms of gp, that is, s n is given by a into 1 minus r to the power n upon 1 minus r, if r is less than 1. a is the first term, r is the common ratio, n is the number of terms. The knowledge of this formula is the key idea in this question. Given gp is 1 minus a a squared minus a cubed, and so on up to n terms. We have to find the sum of n terms of this gp. We have learned in the key idea that sum of n terms of gp, that is, s n, is given by a into 1 minus r to the power n. upon 1 minus r, if r is less than 1. Now here, a, that is, first term is equal to 1, and r is equal to minus a, which is less than 1. So s n is equal to 1 into 1 minus minus a to the power n upon 1 minus minus a. This is equal to 1 minus minus a to the power n upon 1 plus a. Hence, the required sum is 1 minus minus a to the power n upon 1 plus a. This is our required answer. So this completes the session. Bye and take care.