Question

Find the number of terms in the A.P. 3, 6, 9, 12 , ….., 108.​

Answer 1

Answer:

2

n

[2.3+(n−1)3]=108

6n+3n

2

−3n=216

3n

2

+3n−216=0

x

2

+n−72=0

(x+9)(x−8)=0

x=8

Answer 2

Answer:

$first \: term \: \: \: a = 3 \: \: common \: difference \: \: \\ d = 6 - 3 \: \: last \: term \: l = 111 \\ we \: know \: that \: \: \: \: \: n \: = \frac{l - a}{d} + 1 \\ \: \: \: \: \: n = \frac{111 - 3}{3} + 1 = 37 \ \:$