Question

find the 21th term of an a.p whose first two terms are 3 and 4​

Answer 1

21th term = a + 20d

= 3 + 20(1)

= 3 + 20

= 23

21th term = 23....

Answer 2

a=3 ....eq(1)

a+d=4 ....eq(2)

Substitute a=3 in eq(2)

3+d=4

d=1

$\: \: \: \: \: \: \: \: \: \: \: \: t_{21} = a + (n - 1)d \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = 3 + (21 - 1)1 \\ \: \: \: \: \: \: \: = 3 + 20 \\ = 23$

.°. 21st term is 23.