Question

The 21^st term of the AP whose first two terms are –3 and 4 is ______.

Options

• 17

• 137

• 143

• –143

Answer 1

The 21^st term of the AP whose first two terms are –3 and 4 is 137.

Explanation:

First two terms of an AP are a = – 3 and a_{2 =} 4.

We know, nth term of an AP is

a_{n =} a + (n – 1)d

Where,

a = First term

a_n is n^th term

d is the common difference

a_{2 =} a + d

4 = – 3 + d

d = 7

Common difference, d = 7

a_{21 =} a + 20d

= – 3 + (20)(7)

= 137