helo this is a homework problem i got in math 30 pure(adsbygoogle = window.adsbygoogle || []).push({});

i got an answer but i would like to know how to get it by using a formula?

The exercise gose like this:

Initially, a pendulum swings through an arc of 2feet. On each successive swing,the length of the arc is 0.9 of the previous length.

a. Determine the lenght of the arc after 10 swings

i did this to find the answer:

using the formula Sn= a((r^n)-1)/r-1 were

Sn=?

a=2

r=0.9

n=10

Sn=2((0.9^10)-1)/0.9-1

Sn= 13.03 feet.

the aswer will be 13.03 feet

B. On which swing is the lenght of the arc first less than 1 foot?

I got that it was on the 7th swing were it is 0.9565938. but i got it by multipliying the 2feet by 0.9 and then its answer x 0.9 egain and so on ...until it give me an answer lower than 1...

how can i get this by using a formula(wich formula should i use) ??

C. After the 15 swings,Determine the total lenght that the pendulum will have swung.

using the same formula asaI can get this answer but rather than using n=10 it will be n=15

right??

thanks in advance for ur help.

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# Homework Help: Math 30 pure geometric series

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