## anonymous one year ago Find S9 for the series 1 + 5 + 25 + 125 +... i cnt be anything? bc i got 0

1. Michele_Laino

it is a geometric sequence whose first term is a1= 1 and constant q is 5

2. anonymous

okay

3. Michele_Laino

so: $\Large {S_9} = {a_1}\frac{{1 - {q^9}}}{{1 - q}} = 1 \cdot \frac{{1 - {5^9}}}{{1 - 5}} = ...?$

4. anonymous

488281

5. Michele_Laino

that's right!

6. anonymous

Find S10 for the series 1 + 2 + 4 + 8 +... is it the same formula if its not mulitpying by 2?

7. Michele_Laino

here we have: first term= 1 constant= 2 so: $\Large {S_{10}} = {a_1}\frac{{1 - {q^{10}}}}{{1 - q}} = 1 \cdot \frac{{1 - {2^{10}}}}{{1 - 2}} = ...?$

8. anonymous

1023

9. Michele_Laino

correct!