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2 answers:
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Given:
The different recursive formulae.
To find:
The explicit formulae for the given recursive formulae.
Solution:
The recursive formula of an arithmetic sequence is and the explicit formula is
, where a is the first term and d is the common difference.
The recursive formula of a geometric sequence is and the explicit formula is
, where a is the first term and r is the common ratio.
The first recursive formula is:
for
.
It is the recursive formula of an arithmetic sequence with first term 5 and common difference 5. So, the explicit formula for this recursive formula is:
Therefore, the correct option is A, i.e., .
The second recursive formula is:
for
.
It is the recursive formula of a geometric sequence with first term 5 and common ratio 3. So, the explicit formula for this recursive formula is:
Therefore, the correct option is F, i.e., .
The third recursive formula is:
for
.
It is the recursive formula of an arithmetic sequence with first term 5 and common difference 3. So, the explicit formula for this recursive formula is:
Therefore, the correct option is D, i.e., .
Answer:
There are different ways to choose 4 screws such that 2 have a Phillips head and 2 have a slotted head.
Step-by-step explanation:
If 4 screws must be chosen so that 2 have a Phillips head and 2 have a slotted head, then you have to choose 2 screws with a Phillips head from 4 screws with a Phillips head and 2 screws with a slotted head from 4 screws with a slotted head.
You can choose 2 screws with a Phillips head from 4 screws with a Phillips head in
different ways.
You can choose 2 screws with a slotted head from 4 screws with a slotted head in
different ways.
In total there are different ways to choose 4 screws such that 2 have a Phillips head and 2 have a slotted head.