Answer:
a)
i.the lower limit of the sum
: n=1
ii.the upper limit of the sum
: n=18
iii.the explicit formula of the sum
: [tex]a_n=7n-4[/tex]
b) 1,125 beads
Step-by-step explanation:
a) The number of beads per row of Dante's necklace is given by the series:
3 + 10 + 17 + 24 + ...
The first term of this series is [tex]a_1=3[/tex].
There is a constant difference of [tex]d=10-3=7[/tex].
To write this series in summation notation, we need to determine the explicit formula which is given by:
[tex]a_n=a_1+d(n-1)[/tex]
We plug in the values to get:
[tex]a_n=3+7(n-1)[/tex]
[tex]\implies a_n=3+7n-7[/tex]
[tex]\implies a_n=7n-4[/tex]
The summation notation is given by:
[tex]\sum^{18}_{n=1}(7n-4)[/tex]
b) The total number of beads in the necklace is given by the sum of the first 18 terms of the sequence.
This is given by [tex]S_n=\frac{n}{2}(2a_1+d(n-1))[/tex]
We substitute the values to obtain:
[tex]S_{18}=\frac{18}{2}(2\cdot3+7(18-1))[/tex]
[tex]S_{18}=9(6+119)[/tex]
[tex]S_{18}=9(125)[/tex]
[tex]S_{18}=1125[/tex]
Therefore the total number of beads is 1125
