Advertisements
Advertisements
प्रश्न
Which term of the AP 21, 18, 15, …… is -81?
Advertisements
उत्तर
The given AP is 21,18,15,.......
First term, a = 21
Common difference, d= 18 -21 =-3
Suppose nth term of the given AP is - 81. then,
an = -81
⇒ 21 +(n-1) × (-3) =-81 [an = a + (n-1)d]
⇒ -3 (n-1) = -81 -21=-102
⇒ `n-1 = 102/3 = 34`
⇒ n= 34+1=35
Hence, the 35th term of the given AP is -81.
APPEARS IN
संबंधित प्रश्न
The houses in a row numbered consecutively from 1 to 49. Show that there exists a value of x such that sum of numbers of houses preceding the house numbered x is equal to sum of the numbers of houses following x.
The first and the last terms of an AP are 7 and 49 respectively. If sum of all its terms is 420, find its common difference.
Find the sum of first 51 terms of an AP whose second and third terms are 14 and 18 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`]
In an A.P., if the 5th and 12th terms are 30 and 65 respectively, what is the sum of first 20 terms?
Find the sum 25 + 28 + 31 + ….. + 100
Is -150 a term of the AP 11, 8, 5, 2, ……?
If 4 times the 4th term of an A.P. is equal to 18 times its 18th term, then find its 22nd term.
The sum of three consecutive terms of an AP is 21 and the sum of the squares of these terms is 165. Find these terms
The sum of the first n terms of an AP is (3n2+6n) . Find the nth term and the 15th term of this AP.
The next term of the A.P. \[\sqrt{7}, \sqrt{28}, \sqrt{63}\] is ______.
Write the common difference of an A.P. whose nth term is an = 3n + 7.
The 9th term of an A.P. is 449 and 449th term is 9. The term which is equal to zero is
Q.17
Q.20
The sum of first 14 terms of an A.P. is 1050 and its 14th term is 140. Find the 20th term.
How many terms of the A.P. 27, 24, 21, …, should be taken so that their sum is zero?
The sum of first 15 terms of an A.P. is 750 and its first term is 15. Find its 20th term.
The nth term of an A.P. is 6n + 4. The sum of its first 2 terms is ______.
