I honestly don't know any of this so
Answer:
The sequence above is a geometric sequence
For an nth in a geometric sequence

where n is the number of terms
a is the first term
r is the common ratio
From the question
a = 45
r = 15 / 45
The explicit formula for the sequence is
U(n) = 45(1/3)^n-1
Hope this helps you
Answer:
Use multitape Turing machine to simulate doubly infinite one
Explanation:
It is obvious that Turing machine with doubly infinite tape can simulate ordinary TM. For the other direction, note that 2-tape Turing machine is essentially itself a Turing machine with doubly (double) infinite tape. When it reaches the left-hand side end of first tape, it switches to the second one, and vice versa.
Step-by-step explanation:
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