A circle with center on the origin and point on (4,-2)

Step-by-step explanation:

Review the standard equation of a circle with center at (h, k) and radius r:

(x - h)^2 + (y - k)^2 = r^2

A point on (4, -2) has the radius r^2 = (4)^2 + (-2)^2, or r^2 = 20, or r = 2√5.  Knowing the center is at (0, 0), we can write:

x^2 + y^2 = 20, or x^2 + y^2 = (2√5)^2

20

step-by-step explanation:

36 girls

step-by-step explanation:

the 48 boys is 4 parts of the ratio

divide 48 by 4 to obtain one part of the ratio

= 12 ← 1 part of the ratio

3 parts = 3 × 12 = 36 ← number of girls