Question.
Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149.
Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149.
Solution:
$d=7$
$a_{22}=149$
\mathrm{S}_{22}=?
$a_{22}=a+(22-1) d$
149 = a + 21 × 7
149 = a + 147
a = 2
$S_{n}=\frac{n}{2}\left(a+a_{n}\right)=\frac{22}{2}(2+149)=11(151)=1661$
$d=7$
$a_{22}=149$
\mathrm{S}_{22}=?
$a_{22}=a+(22-1) d$
149 = a + 21 × 7
149 = a + 147
a = 2
$S_{n}=\frac{n}{2}\left(a+a_{n}\right)=\frac{22}{2}(2+149)=11(151)=1661$
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