Find the inverse of f if f(x) = x^2 - 8x + 8 and x is less than or equal to 4

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SUMMARY

The inverse of the function f(x) = x² - 8x + 8, defined for x ≤ 4, is determined by first setting y = x² - 8x + 8 and then switching x and y. This leads to the equation x = y² - 8y + 8. By rearranging and completing the square, the equation simplifies to (y - 4)² = x + 8. The final expression for the inverse function is f⁻¹(x) = 4 ± √(x + 8), with the domain of f⁻¹(x) being x ≥ -8, reflecting the range of the original function f(x).

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Homework Statement


Find f^{-1}(x) if f(x)=x^{2}-8x+8 and x\leq4

The Attempt at a Solution


I set y=x^{2}-8x+8, and then switch y and x to get x=y^{2}-8y+8.
I then try solving for y, but I end up with y's on both sides of the equation:

x=y^{2}-8y+8

x-8=y^{2}-8y

x-8=y(y-8)

\frac{x-8}{y-8}=y

?
 
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It's a quadratic equation in y, so try the quadratic formula :-)
 
or complete the square.

x-8=y^{2}-8y

x-8+16=y^{2}-8y+16

x+8=(y-4)^2

   

Don't forget the ± when taking the square root.

The range of a function's inverse, f -1(x), is the same as the domain of the function, f(x).
 

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