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Question 21
Question:
(pq)th term and the sum of pq terms.
Answer: Let a = first term, d = common difference


Subtract (ii) from (i)










Question 22
Question: 

Answer: 





Question 23
Question: The sum of n terms of three APs are S1,S2 and S3. The first term of each is 1 and common differences are 1, 2 and 3 respectively. Prove that S1 + S3 = 2S2.
Answer: 



Question 24
Question: The first and the last term of an AP are a and l respectively. If S denotes the sum of terms show that the common 
Answer: a = first term, l = last term, Sn = S|, d = common difference.



Question 25
Question: The ratio of the sums of m and n terms of an AP is 
Show that the ratio of mth and nth terms is (2m - 1) : (2n - 1).
Answer: 




Question 26
Question: If the sums of the first p, q, r terms of AP are a, b, c respectively prove that

Answer: 








Question 27
Question: If a, b, c are in AP, show that (a - c)2 = 4(b2 - ac).
Answer: 

Question 28
Question: If a2 + 2bc, b2+ 2ca, c2 + 2ab are in AP, show that 
Answer: 






Question 29
Question: Two cars start together in the same direction at the same place. The first goes with uniform speed of 15 km/hr, the second goes at the speed of 10 km/hr in the first hour and increases the speed by 0.1 km each succeeding hour. After how many hours will the second car over take the first if both cars go non stop?
Answer: Speed of second car = 10 km/hr
Uniform Speed of the first car = 15 km/hr
The second car increases its speed by 1 km every hour.



Since both cars are travelling in the same direction, the distance covered will be same.

They are together initially or after 11 hours. Thus the second car over takes the first car after 11 hours of journey.
Question 30
Question: Find the indicated terms in the following G.P.:



iv. Find the 12th term if a GP of which the 5th and 9th terms 
Answer: 








iv. Find the 12th term if a GP of which the 5th and 9th terms are 
Let a = first term, r = common ratio





