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Arithmetic Progressions

Question 2:

Find the sums given below

(i) 7 + + 14 + ………… + 84

(ii) 34 + 32 + 30 + ……….. + 10

(iii) − 5 + (− 8) + (− 11) + ………… + (− 230)

Answer:

(i)7 + + 14 + …………+ 84

For this A.P.,

a = 7

l = 84

Let 84 be the nth term of this A.P.

l = a + (n − 1)d

22 = n − 1

n = 23

We know that,

(ii)34 + 32 + 30 + ……….. + 10

For this A.P.,

a = 34

d = a2a1 = 32 − 34 = −2

l = 10

Let 10 be the nth…

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