Question

If the 10 term of an ap is 21 an d the sum of its first ten terms is 120 ,find its an term

Answer 1

Solution:

Given: Tenth term of an AP is 21
which means,        $a_{10}= 21$     
The sum of first ten terms of the AP equals 120,
which means,        $S_{10}=120$

BY using the formula of $S_n=n(a+l)/2$,

               [tex]S_{10}= 10(a+21)/2 [/tex]
               $120=5(a+21)$
               $a+21=24$
               $a=24-21$
               ∴$a=3$     Hope it helps