Question

find a function whose graph is the given curve:
the bottom half of a circle x^2+y^2=16

Answer 1

if you solve that for y, what do you get

Answer 2

x^2+y^2=16

y^2 = 16 - x^2

y = +/- sqrt( 16 - x^2 )

now you have two graphs here

y = sqrt(16 - x^2)
y = - sqrt(16 -x^2)

determine which one is the bottom half