Geometric Sequences C2

Original post by bg***j2

Hello! I'm stuck on a geometric question :frown:

A geometric series begins 420 + 294 +205.8 +...

Worked out that r=0.7, sum to infinity is 1400.

Question: Write the nth term of the series in the form p x q^n, where p and q are constants.

Thanks!

Surely you know that: (for GPs)

\ u_n = u_1 r^{n-1}

?

Reply 2

Segadfx

5

Full solution:

Spoiler

(edited 10 years ago)

Reply 3

OP

I got 420 x 0.7^n-1. Is that right? Wasn't sure whether 'n-1' was allowed..

Reply 4

Original post by bg***j2

I got 420 x 0.7^n-1. Is that right? Wasn't sure whether 'n-1' was allowed..

You can multiply 420 bysomething to get rid of the n-1, can you see what? :smile:

Reply 5

OP

294 x 0.7^n ? :redface:

Reply 6

Segadfx

5

Original post by bg***j2

294 x 0.7^n ? :redface:

Hey, just edited my original post which should show you all of the steps. Hope it helps! If you need further explanation just quote me.

Reply 7

OP

Ohh I see, thank you!

Reply 8

Original post by Segadfx

.

Just for future reference, full solutions ought only be given if absolutely necessary, and big hints should also be spoilered. :smile:

Reply 9

OP

I have another question :colondollar:

Describe the geometrical transformation that maps the graph of y = 2^x onto the graph of y = 2^4x-3

Initially I thought it was a translation x direction [3 0] (0 being the y).

but the mark scheme says translation x direction [3/4 0]

Can someone explain this please

Reply 10

Segadfx

5

Original post by joostan

Just for future reference, full solutions ought only be given if absolutely necessary, and big hints should also be spoilered. :smile:

Ah, I just read the stickied threads at the top. My misunderstanding.

Reply 11

Original post by Segadfx

Ah, I just read the stickied threads at the top. My misunderstanding.

No harm done :smile:

Reply 12