Advertisements
Advertisements
प्रश्न
Find the sum of 28 terms of an A.P. whose nth term is 8n – 5.
Advertisements
उत्तर
nth term of an A.P. = tn = 8n – 5
Let a be the first term and d be the common difference of this A.P.
Then,
a = t1
= 8 × 1 – 5
= 8 – 5
= 3
t2 = 8 × 2 – 5
= 16 – 5
= 11
∴ d = t2 – t1
= 11 – 3
= 8
The sum of n terms of an A.P. = `S = n/2 [2a + (n - 1)d]`
`=>` Sum of 28 terms of an A.P. = `28/2 [2 xx 3 + 27 xx 8]`
= 14[6 + 216]
= 14 × 222
= 3108
APPEARS IN
संबंधित प्रश्न
If 12th term of an A.P. is –13 and the sum of the first four terms is 24, what is the sum of first 10 terms?
If the 8th term of an A.P. is 37 and the 15th term is 15 more than the 12th term, find the A.P. Also, find the sum of first 20 terms of A.P.
The 4th term of an AP is zero. Prove that its 25th term is triple its 11th term.
Write an A.P. whose first term is a and common difference is d in the following.
a = –19, d = –4
In an A.P. 19th term is 52 and 38th term is 128, find sum of first 56 terms.
Write the common difference of an A.P. whose nth term is an = 3n + 7.
Find the sum of three-digit natural numbers, which are divisible by 4.
Find the sum of odd natural numbers from 1 to 101.
Find t21, if S41 = 4510 in an A.P.
The sum of the first five terms of an AP and the sum of the first seven terms of the same AP is 167. If the sum of the first ten terms of this AP is 235, find the sum of its first twenty terms.
