Question

Find the general term a.n for the geometric sequence
a1 = -5 and a2 = 10

Answer 1

@jim_thompson5910 can you help

Answer 2

r = a2/a1

r = ??

Answer 3

r = -2

Answer 4

r = -2 good

Answer 5

so your nth term is

an = a1*r^(n-1)

an = -5*(-2)^(n-1)

Answer 6

would it be an = -5n(-2n + 2)??
@jim_thompson5910

Answer 7

Sorry -5(-2n + 2)

Answer 8

no you don't distribute, you just leave it as

\[\Large a_{n} = -5(-2)^{n-1}\]

Answer 9

thank you! @jim_thompson5910

Answer 10

yw

Answer 11

So first find the common ratio.
\[r = \frac{ a _{n} }{ a _{n-1} }\]
\[r = \frac{ 10 }{ -5 }\]
\[r = -2\]

Now plug into the Formula.
\[a _{n} = a _{1} \times r ^{n-1}\]
\[a _{n} = -5 (-2) ^{n-1}\]

Answer 12

thank you @some_someone