The answer to this question is D.
You subtract 6 every time. So, there are already 3 terms, so we need to find the next 19. We can do 19x6, which equals 114. Then subtract 114 from 7, which is -107.
So, the 22nd term will be -107. Hope this helps :)
The expression for a in terms of c is
. The correct option is the third option 
<h3>Pythagorean theorem </h3>
From the question, we are to determine the expression for a in terms of c
In the given right triangle, we can write that
(<em>Pythagorean theorem</em>)
Thus,



Hence, the expression for a in terms of c is
. The correct option is the third option 
Learn more on Pythagorean theorem here: brainly.com/question/23994492
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