Question

3. Find the 18th and 25th terms of the sequence defined by

Answer 1

Hi,

It is given that ,

an = n( n +3 ) , if n € N and n is even ,

i ) if n = 18 ( even )

a18 = 18( 18 + 3 )

= 18 × 21

= 378

a 18 = 378

ii ) if n = 25 ( odd )

it is given that ,

an = 2n/ ( n² + 1 )

a 25 = ( 2 × 25 ) / ( 25² + 1 )

= 50/ ( 625 + 1 )

= 50/626

= 25/313

Therefore ,

a15 = 378 ,

a 25 = 25/313

I hope this helps you.

: )