f(x) = -x + b is its own inverse because f(f(x)) = x
f(f(x)) = -f(x)+b = -(-x+b)+b = x
I have another question here...
Explain why any equation of the form y = -x + b is its own inverse. Use both algebraic and graphics arguments.
What do they mean by 'is its own inverse'? Its its own inverse without switching the y and x, and just the - sign?