Question

the 21st term of the AP whose first two terms are -3 and 4 is​

Answer 1

Hi !

First term ' a ' = - 3

second term = 4

d = t2 - t1 = 4 - ( -3) = 7

Since,

using formula

tn = a + ( n - 1 ) d

t21 = a + 20d

t21 = -3 + ( 20 * 7)

t21 = -3 + 140 .

t21 = 137 Answer ✔

____________________________

Hope this helps !.

@Rajukumar111

Answer 2

137

Given:

The first term of the AP = - 3

Calculating the common difference of the AP

= 4 - (- 3)

= 4 + 3

= 7

The formula that is used to calculate the n terms of an AP:

An = a + (n - 1) d

Substituting all the values which are known to us in this formula we get:

= - 3 + (21 - 1) (7)

= - 3 + (20) (7)

= - 3 + 140

= 137

Therefore, the 21 st term of the Arithmetic Progression is 137.