A boy is building a pyramid out of building blocks. He puts 20 blocks in the first row, then he puts 19 blocks in the row above,
1 answer:
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9514 1404 393
Answer:
sum = ∑[n=1,5] 4^(n-4)
Step-by-step explanation:
First of all, you need to be able to describe the n-th term.
Here, we have ...
term #: 1, 2, 3, 4, 5
value: 4^-3, 4^-2, 4^-1, 4^0, 4^1
That is, the exponent of 4 is 4 less than the term number. So, the n-th term is 4^(n-4). The sum of the 5 terms shown is then ...