In arithmetic progressions of exercise 5.3 of math, how i solve this important question in best way, please help me for solving this problem Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149.
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Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149. Q.7
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Given,
Common difference, d = 7
22nd term, a22 = 149
Sum of first 22 term, S22 = ?
By the formula of nth term,
an = a+(n−1)d
a22 = a+(22−1)d
149 = a+21×7
149 = a+147
a = 2 = First term
Sum of n terms,
Sn = n/2(a+an)
S22 = 22/2 (2+149)
= 11×151
= 1661