Question

Find the sum of first 22 terms of an AP in which d = 7 and 22nd term is 149.​

Answer 1

Step-by-step explanation:

formula: n/2(2a+(n-1)d)

or n/2(first term +last term)

here last is 149

first=149-7×22=-6

so sum is 11×(-6+149)

=143×11

=1573

this is the basic idea to solve fastly.

Answer 2

Answer: 1661

Step-by-step explanation:

Given

d = 7

22nd term = 149

a+21d = 149

a + 21(7) = 149

a + 147 = 149

a = 2

using formula: Sn = (n/2) [2a + (n - 1) d]

S₂₂ = (22/2) [ 2 × 2 + (22 - 1)7 ]

S₂₂ = 11 [4 + 21(7)]

S₂₂ = 11 [4 + 147]

S₂₂ = 11 × 151

S₂₂ = 1661

Thus, the sum of first 22 terms is 1661.