Question

The sum of n${}^{th}$ terms of an A.P is 5n - 3n. Find the A.P . Hence find its 10th term.

Answer 1

Putting $n=1,$ $5n^2-3n$

$=5-3=2$

putting $n=2,$ $5n^2-3n$

$5\times 2^2-3\times 2$ $=14$

therefore $2nd$ term is $14-2=12$

therefore $A.P$ is $2,12,\mathrm{22....}$ and so on$.$

$10th$ term $=a+9d$

$=2+9\times 10$

$=2+90$

$=92.$