Answer:
It's a rotation of 90 degrees - doesn't matter which way - around the intersection of the two lines
Step-by-step explanation:
Claim: it's a 90 degree rotation around the intersection of f and g.
It's easy to spot the two lines are perpendicular. Let's assume the rotation doesn't happen at the point of intersection [tex]x_0[/tex], but slightly to the side, around let's say, [tex]x_0+\epsilon[/tex]; the new line will coincide with [tex]g(x)[/tex] if and only if [tex]\epsilon = 0[/tex], ie only the rotation happens around the intersection.