Question

Dada a pa (a1,a2,a3,....) onde a15=6 e r=-3 determine a10 - a4

Answer 1

$a_{15} = a_{10} + 5r \\ a_{15} =a_{4} + 11r \\ \\ 6 = a_{10} + 5 \times ( - 3) \\ 6 = a_{4} + 11 \times ( - 3) \\ \\ 6 = a_{10} - 15 \\ 6 = a_{4} - 33 \\ \\ a_{10} = 21 \\ a_{4} = 39 \\ \\ a_{10} - a_{4} = 21 - 39 = - 18$