Question

Find the 20th term of the AP
whose 3rd term is 7 and the
7th term exceeds 3 times the
2.
3rd term by​

Answer 1

Step-by-step explanation:

3rd term = 7

a3 = a+ 2d

7 = a + 2d............ ( 1 )

7th term = 3 * 7

7th term = 21

a7 = 6d

21 = a + 6d............. (2)

By subtracting equation ( 1 ) and equation ( 2 )

21 = 6d

7 = 2d

( - ) ( - )

---------------

14 = 4d

4d = 14

d = 14/4

d. 7/2

d = 3.5

By putting d = 3.5 in equation ( 1 )

7 = a + 2d

7 = a + 2 ( 3.5 )

7 = a + 2*3.5

7 = a + 7

a = 7 - 7

a = 0

20 th term,

a20 = a +19d

a20 = 0 + 19*3.5

a20 = 0 + 66.5

a20 = 66.5