Question

if an=5+(n-1)3,find a20​

Answer 1

The 20th term of an AP, $a_{20}$ = 62

Step-by-step explanation:

We have,

$a_n$ = 5 + (n - 1)3

To find, the value of $a_{20}$ = ?

Put n = 1, 2, 3, 4, ...

The 1st term of an AP ( n = 1)

$a_1$ = 5 + (1 - 1)3 = 5 + 0 = 5

The 2nd term of an AP ( n = 20)

$a_2$ = 5 + (2 - 1)3 = 5 + 3 = 8

The 3rd term of an AP ( n = 3)

$a_3$ = 5 + (3 - 1)3 = 5 + 6 = 11

...

The 20th term of an AP ( n = 20)

$a_{20}$ = 5 + (20 - 1)3 = 5 + (19)3 = 5 + 57 = 62

∴ The 20th term of an AP, $a_{20}$ = 62