Given data:
The first point in the graph is (a, b)=(5,0).
The second point on th graph is (c,d)=(0,-5).
The expression for the equaion of the line passing through the given points is,
y-b= (d-b)(x-a)/(c-a).
Substitute the given values in the above expression.
y-0=(-5-0)(x-5)/(0-5)
y=x-5
The above expression can be written as,
x=y+5
To get the inverse of the function replace y by x in the above expression.
f^(-1)(x)=x+5
Thus, the inverse of the given function is x+5.