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 a₂ = 4

We know, n^th 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

a₂ = a + d

4 = – 3 + d

d = 7

Common difference, d = 7

a₂₁ = a + 20d

= – 3 + (20)(7)

= 137