Advertisements
Advertisements
प्रश्न
For an A.P., if t1 = 1 and tn = 149, then find Sn.
Activitry :- Here t1= 1, tn = 149, Sn = ?
Sn = `n/2 (square + square)`
= `n/2 xx square`
= `square` n, where n = 75
Advertisements
उत्तर
Here, t1= 1, tn = 149, Sn = ?
Sn = \[\frac{n}{2} (\boxed{t_1} + \boxed{t_n})\]
= `n/2 (1 + 149)`
= \[\frac{n}{2} \times \boxed{150}\]
= \[\boxed{75}\] n, where n = 75
APPEARS IN
संबंधित प्रश्न
If the ratio of the sum of first n terms of two A.P’s is (7n +1): (4n + 27), find the ratio of their mth terms.
The ratio of the sums of m and n terms of an A.P. is m2 : n2. Show that the ratio of the mth and nth terms is (2m – 1) : (2n – 1)
A spiral is made up of successive semicircles, with centres alternately at A and B, starting with centre at A of radii 0.5, 1.0 cm, 1.5 cm, 2.0 cm, .... as shown in figure. What is the total length of such a spiral made up of thirteen consecutive semicircles? (Take `pi = 22/7`)
[Hint: Length of successive semicircles is l1, l2, l3, l4, ... with centres at A, B, A, B, ... respectively.]
A small terrace at a football field comprises 15 steps, each of which is 50 m long and built of solid concrete. Each step has a rise of `1/4` m and a tread of `1/2` m (See figure). Calculate the total volume of concrete required to build the terrace.
[Hint: Volume of concrete required to build the first step = `1/4 xx 1/2 xx 50 m^3`]
Find the sum of first 8 multiples of 3
Find the sum of all integers between 100 and 550, which are divisible by 9.
Find the sum of the first 51 terms of the A.P: whose second term is 2 and the fourth term is 8.
Determine the A.P. Whose 3rd term is 16 and the 7th term exceeds the 5th term by 12.
If an denotes the nth term of the AP 2, 7, 12, 17, … find the value of (a30 - a20 ).
The sum of the first n terms of an AP is (3n2+6n) . Find the nth term and the 15th term of this AP.
If Sn denotes the sum of the first n terms of an A.P., prove that S30 = 3(S20 − S10)
Write the nth term of an A.P. the sum of whose n terms is Sn.
Let Sn denote the sum of n terms of an A.P. whose first term is a. If the common difference d is given by d = Sn − kSn−1 + Sn−2, then k =
If 18, a, b, −3 are in A.P., the a + b =
The sum of n terms of an A.P. is 3n2 + 5n, then 164 is its
The common difference of the A.P.
Q.12
How many terms of the series 18 + 15 + 12 + ........ when added together will give 45?
In an A.P. sum of three consecutive terms is 27 and their products is 504. Find the terms. (Assume that three consecutive terms in an A.P. are a – d, a, a + d.)
