You can square the whole problem to cancel out the square root. Might make things easier.
Answer:

Step-by-step explanation
The standard equation of a circle centered at origin is 
r = radius of the circle
The circle is passing through the point (0,5)
∴ radius 



∴ The equation of the circle is

What is the slope of the line in the graph show below? c1
Before the mechanic worked on it, it cost .09 (cents) per mile. After the mechanic worked on it, it cost .08 (cents) per mile. Divide the number of gallons by the miles in each case and multiply the result by 4.