Regarding last question.

i never learnt that formula we have been using and for all other questions used 1 of two formulas sn=t1(r^n-1) / r-1 or sn=rtn-t1 / r-1

 

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# 14 in the pre calculus textbook in Alberta 

 

suppose a set of 10 beads were laid in a line where each successive bead had a diameter that was 3/4 of the diameter of the previous bead. If the first bead had a diameter of 24mm, determine the total length of the line of the beads. Express your answer to the nearest millimetre.

12 minutes ago

Answered By Alex V

If I'm understanding this correctly you need to set up a sum series function: 

  $\sum_{x=0}^9=24mm\left(\frac{3}{4}\right)^x$∑x=09=24mm(34 )x  

Note that the end of the series is 9, because for many series calculations the end of the series is (x-1). 

Plug this formula into your calculator, or an excel sheet if you can, and you should get an answer of 90.59mm which makes the answer: Distance = 91mm.

7 years ago

Answered By Xuezhong J

if you have not learned this formula, do like below:

_{S=24+24*(3/4)+24*(3/4)²+...+24*(3/4)⁹}                       ?1?

from 1,  you can get:

s₁₀ *(3/4)=24*(3/4)+24*(3/4)² +...+24*(3/4)⁹+24*(3/4)¹⁰        (2)

 

Then (1)-(2), you get:

s₁₀*(1-3/4)=24-24*(3/4)¹⁰

So, S₁₀=24*(1-(3/4)⁹)/(1-3/4)

the answer is the same.

Attached Whiteboard:

  Play Drawing

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7 years ago

Answered By Xuezhong J

S₁₀=24*(1-(3/4)¹⁰)/(1-3/4), this is corret answer.

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