Question

21. The sum of first 7 terms of an A.P. is 10 and that of next 7
terms is 17. Find the progression.​

Answer 1

Answer:

1 , 8/7 , 9/7 , 10/7 ........

Step-by-step explanation:

sum of AP = n/2 ( 2a + (n-1)d )

10=7/2( 2a + (7-1 ) d )

20 = 7 ( 2a + 6d)

20= 14a + 42 d. ( divide both sides by 2 )

10 = 7a + 21d ------- 1

for next seven terms

à = a + 7d

sum = n/2 ( 2à + (n-1) d )

17 = 7/2 ( 2a + 14d + 6d)

34.= 7 ( 2a + 20d ) ( divide both sides by 2.)

17 = 7a + 70d --------2

2 -- 1

17-10 = 7a +70d - 7a - 21 d

7 = 49 d

d = 1/7

substituting d in equation 1

10 = 7a + 21(1/7 )

10 = 7a + 3

7a =7

a=1

therefore the progression is:

1 , 8/7 , 9/7 ........

Thanks