Question

If n th term is (2n-5) then find ten th term of an ap

Answer 1

Answer:-

Answer is 15 .

Given:- The nth term of an Ap is ( 2n - 5 )

To Find:- The 10th term of an Ap

Solution:-

tn = 2n - 5

so , putting n = 1 , 2 , 3 we get

t1 = 2 × 1 - 5 = 2 - 5 = - 3

t2 = 2 × 2 - 5 = 4 - 5 = -1

t3 = 2 × 3 - 5 = 6 - 5 = 1

So ,

a1 ( 1st term ) = -3

a2 ( 2nd term ) = -1

a3 ( 3rd term ) = 1

Now , Common difference (d) = (a2 - a1)

⇒ d = [ -1 - ( -3)]

⇒ d = [-1 + 3]

⇒ d = 2

t10 = a + ( n -1 ) d

t10 = -3 + ( 10 - 1 ) 2

t10 = -3 + 9 × 2

t10 = -3 + 18

t10 = 15

$\therefore{t10 = 15}$