Check the forward differences of the sequence.
If
, then let
be the sequence of first-order differences of
. That is, for n ≥ 1,

so that
.
Let
be the sequence of differences of
,

and we see that this is a constant sequence,
. In other words,
is an arithmetic sequence with common difference between terms of 2. That is,

and we can solve for
in terms of
:



and so on down to

We solve for
in the same way.

Then



and so on down to


Answer: Arc
Explanation: An arc is a segment of a curve.
<span>Eu preciso de pontos, então você pode manter isso por favor</span>
She forgot about the final x at the end, because the first expression is 3x+6+x, and the second one is 3(x+2). The second one expands to 3x+6, but it doesn't have the final term at the end.
Also, 3 is not really a factor of x (technically it could be because x in unknown, but in terms of like terms and stuff it isn't) so you can't take a 3 out of x (unless you leave it as 1/3x I guess).
Anyway, yeah she forgot about the final x and therefore the factor she took out is incorrect anyway. She also could've simplified the first expression so that it became 4x + 6