Question

Find the 21st term of an AP whose first two term are -3 and 4

Answer 1

The first two terms of AP are
-3 , 4

a = -3
d = 4+3
d = 7

A21 = a + 20d
= -3 + 20 × 7
= -3 + 140
= 137.

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Answer 2

Answer:

The 21st term of an AP is 137.

Step-by-step explanation:

It is given that first two term are -3 and 4.

Here first term is -3 and common difference is

$d=a_2-a_1=4-(-3)=7$

The nth term of an AP is

$a_n=a+(n-1)d$

$a_{21}=-3+(21-1)(7)$

$a_{21}=-3+(20)(7)$

$a_{21}=-3+140$

$a_{21}=137$

Therefore the 21st term of an AP is 137.