Question

The 7th term of an AP is 39 and 17th term is 69 then find series.

Answer 1

Answer:

series =(21,24,27,30,33,36,39,........)

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Answer 2

Answer:

s7=39.

s17=69.

sn=n/2[2a+(n-1)d].

s7=7/2[2a+(7-1)d].

39=7/2[2a+6d].

39/7=a+6d.......(1).

sn=n/2[2a+(n-1)d].

s17=17/2[2a+(17-1)d].

69=17/2[2a+16d.

69/17=a+16d......(2).

Substracting (1) from (2).

663-483/119=10d. (Because LCM of 7 & 17=119).

180/119=10d.

d=180/119/10.

d=18/119.

From equation (1).

a+6d=39/7.

a+6(18/119)=39/7.

a+108/119=39/7.

a=39/7-119/108.

a=4212-833/756. (Because LCM of 7 & 108 is 756).

a=3379/756.

I think this is your answer.