I believe the answer to this is correct and i believe he did this by adding(i think)
Using the Pythagorean Theorem,
radius^2 = 40^2 + 9^2
radius^2 = 1,600 + 81
radius^2 = 1,681
radius = 41
Answer: y
=
−
2
x
+
1
This is because slope intercept from is "Y= mx+b" :)
Slope =1/2x hopefully this helps