f(x) = M_X + B for all real numbers.
What is f^{-1}(x), the inverse of f(x)?
X_OVER_M - B_OVER_M
M_X - BM_X + BB_X + MM_OVER_X + BX_OVER_M + BX_OVER_M - BX_OVER_M - M_OVER_BX_OVER_M + B_OVER_MX_OVER_NEG_M - B_OVER_MX_OVER_NEG_M + B_OVER_Mf(x) = M_X + B for all real numbers.
Write an expression for f^{-1}(x), the inverse of f(x).
f^{-1} =
x / M - B / M
y = f(x), so solving for x in terms of y gives x=f^{-1}(y)
f(x) = y = M_X + B
y + -B = M_X
Y_OVER_M - B_OVER_M = x
x = Y_OVER_M - B_OVER_M
So we know: f^{-1}(y) = Y_OVER_M - B_OVER_M
Rename y to x: f^{-1}(x) = X_OVER_M - B_OVER_M
Notice that f^{-1}(x) is just f(x) reflected across the line y = x.