Question

in an ap the third term is 21 and the nineth term is 39 then find tewelth term​

Answer 1

Answer:

a+8d=39

a+2d=21

subtract them

6d=18

d=3

then a=15

12th term = a+11d

= 15+11(3)

=48

Answer 2

EXPLANATION.

=> The third term of an Ap = 21

=> The ninth term of an Ap = 39.

To find the 12th term.

Formula of Nth term of an Ap

=> An = a + ( n - 1 ) d.

=> a + 2d = 21 .......(1)

=> a + 8d = 39 ......(2)

From equation (1) and (2) we get,

=> - 6d = - 18

=> d = 3

Put the value of d = 3 in equation (1)

we get,

=> a + 2(3) = 21

=> a + 6 = 21

=> a = 15

Therefore,

12 th term of an Ap

=> a + 11d

=> 15 + 11(3)

=> 15 + 33

=> 48

12th term of an Ap = 48.