find inverse function
y = f(x) = -3x^2 + 5
write x in terms if y
x = sqrt(-(y-5)/3)
inverse function is
f-1(x) = sqrt(-(x-5)/3)
domain of inverse is the range of the function
from inverse, inside sqrt must greater than or equal to 0 so that x-5 <= 0 which is x <= 5
