Answer:
Mark point E where the circle intersects segment BC
Step-by-step explanation:
Apparently, Bill is using "technology" to perform the same steps that he would use with compass and straightedge. Those steps involve finding a point equidistant from the rays BD and BC. That is generally done by finding the intersection point(s) of circles centered at D and "E", where "E" is the intersection point of the circle B with segment BC.
Bill's next step is to mark point E, so he can use it as the center of one of the circles just described.
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<em>Comment on Bill's "technology"</em>
In the technology I would use for this purpose, the next step would be "select the angle bisector tool."
Subtract 89 from -42. k=-131
Square root is not defined to for negative values. For negative values, the answer of square root is a complex number which is not in Real Domain.
So any such values, for which the expression is not defined are not in the Domian. So the domian of square root of x will be All real numbers greater than or equal to 0.
This can be expressed as:
[0 , ∞)
or
x ≥ 0
The slope (or average rate of change) formula is:

. It is easy to remember as "slope is easy and fun, rise over run" where the y-values of the 2 points would be the "rise" and the x-values of the 2 points would be the "run" So with two points, you label one point as

and the other as

. Then you insert these points into the slope formula (m represents slope). So,

where (-3,6) is x2 and y2 and (5,1) is x1 and y1. It would simplify to

.