Question

The sum of 6th and 10th term of an ap is 66. Find The sum of first 15th term of this sequence

Answer 1

Answer:

The 4^th term of A.P. is 22...

MATHS

The 4

th

term of A.P. is 22 and 15

th

term is 66. Find the first term and the common difference. Hence find the sum of the series to 8 terms.

EASY

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VIDEO EXPLANATION

ANSWER

Let a be the first term and d be the common difference of the A.P.

Now, 4

th

term of the A.P. = a+3d=22 ... (1)

Also, 15

th

term of the A.P. = a+14d=66 ... (2)

Subtracting (1) from (2), we get

11d=44⟹d=4

Substituting value of d in (1), we have

a+12=22⟹a=10

Sum of first 8 terms =

2

n

(2a+(n−1)d)=

2

8

(20+(8−1)4)=192

Hence, the first term, the common difference and the sum upto 8 terms are 10,4 and 192 respectively.