Question

find the 20th term of an AP whose 3rd term is 7 and the seventh term exceeds three times the 3rd term by 2. also find its 'n'th term ​

Answer 1

Answer:

20th term= 75

nth term= 4n-5

Explanation:

3rd term = a+2d =7 - - - - - (1)

And, a+6d = 3(a+2d) +2

=> a+6d = 3a + 6d +2

=> a - 3a = 2

=> - 2a =2

=> a= - 1

Putting the value of a in eq. (1),

a+2d=7

=> - 1+ 2d =7

=> 2d=8

=> d =4

So, 20th term = a+19d

= - 1 + 19(4)

= - 1+ 76

= 75

And the nth term,

= a+ (n-1)d

= - 1 +(n-1)4

= - 1 + 4n - 4

= 4n - 5 ANS...