The sequence a1, a2, a3 ... an .... is such that an=(an-1 + an-2)/ 2 for an >= 3
If a3 = 4 and a5 = 20, what is the value of a6 ?
Please assist!! thanks in advance
$\displaystyle a_5 = \frac{a_4-a_3}{2}$
$\displaystyle 20 = \frac{a_4-4}{2}$
$\displaystyle 40 = a_4-4$
$\displaystyle 40+4 = a_4$
Now you have $\displaystyle a_4$ you can find $\displaystyle a_6$ from
$\displaystyle a_6 = \frac{a_5-a_4}{2}$
Good luck!