Question

Which formula does NOT describe the sequence 8, 6, 3, –1, –6, … ?

an = –0.5n2 – 0.5n + 9

an = an – 1 – n where a1 = 8

an = –0.5n2 – n + 9

None of the formulas describe the sequence.
@jabez177

Answer 1

@Michele_Laino

Answer 2

hint:
let's consider the third formula:
\[\Large {a_n} = - \frac{{{n^2}}}{2} - n + 9\]
Now, if I replace \(n=1\), I get:
\[\Large {a_1} = - \frac{1}{2} - 1 + 9 = - \frac{3}{2} + 9 = \frac{{15}}{2}\]
which is different from \(8\). So, what can you conclude?

Answer 3

Im kinda confused about this @Michele_Laino

Answer 4

hint:
the third formula can not describe the sequence, since its first term is not equal to the first term of the given sequence

Answer 5

Oh so c is the answer?

Answer 6

yes!

Answer 7

Thank You