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Question
If a = 6 and d = 10, then find S10
Solution
a = 6 and d = 10 ......[Given]
Since Sn = `"n"/2[2"a" + ("n" - 1)"d"]`,
S10 = `10/2 [2(6) + (10 - 1)(10)]`
= 5[12 + 9 (10)]
= 5(12 + 90)
= 5(102)
= 510
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Q.10
Q.17
Find the sum of first 20 terms of an A.P. whose first term is 3 and the last term is 57.
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Find the sum of first 1000 positive integers.
Activity :- Let 1 + 2 + 3 + ........ + 1000
Using formula for the sum of first n terms of an A.P.,
Sn = `square`
S1000 = `square/2 (1 + 1000)`
= 500 × 1001
= `square`
Therefore, Sum of the first 1000 positive integer is `square`
Find the sum of last ten terms of the AP: 8, 10, 12,.., 126.
Find the sum of first seven numbers which are multiples of 2 as well as of 9.
Solve the equation
– 4 + (–1) + 2 + ... + x = 437
If the last term of an A.P. of 30 terms is 119 and the 8th term from the end (towards the first term) is 91, then find the common difference of the A.P. Hence, find the sum of all the terms of the A.P.
If the first term of an A.P. is p, second term is q and last term is r, then show that sum of all terms is `(q + r - 2p) xx ((p + r))/(2(q - p))`.
