Answer:
159 degrees
Step-by-step explanation:
A full semicircle (or half circle) has a degrees of 180. And x is equal that semicircle so x = 180, now if we subtract 21 from 180 we get 159, so X = 159.
The answer to this question should be -2x
the answer for this question is x=4
<u>c) 3, 6, 9 12</u> is NOT a geometric progression
<h3>Further explanation
</h3>
Geometry sequences are series of numbers that have a constant ratio
or can be interpreted:
Each number is obtained by multiplying the previous number by a constant
The sequence can be:
a, ar, ar², ar³, ... etc.
Can be formulated
where:
a is the first term, and
r is the common ratio
So we have to see the series has the same ratio or not
a. 
b. 
c.
d. 
<h3>Learn more
</h3>
a geometric sequence
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Determine whether the sequence below is a geometric
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the formula for a finite geometric series
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Keywords : a geometric sequence, the first term, the common ratio
It's along the number line