Question

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

Answer 1

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

Explanation:

For an AP the nth term is T_n = a + (n – 1)d. 

Here a = –3 and the second term is 4, so the common difference d = 4 – (–3) = 7. 

Thus T₂₁ = –3 + (21 – 1) × 7 

= –3 + 20 × 7 

= –3 + 140 

= 137