to find invers
1. solve for y
2. replace y with xinverse
so
x=4-4y+y^2
reorder right side
x=y^2-4y+4
factor right side
x=(y-2)^2
squaer root both sides
+/-√x=y-2
add 2 to both sides
2+/-√x=y
switch x and y
2+/-√y=xinverse
xinverse=2+√y or 2-√y
subtract 4 from both sides
