Question

Use the following graph of the quadratic function f(x)=−18(x−1)2+1 to answer the question. A downward-opening parabola that passes through (negative 2, 0), (1,1) & (4, 0).© 2018 StrongMind. Created using GeoGebra. Which line proves that f(x) does not have an inverse function?

Answer 1

If a horizontal line intersects the graph of f(x) more than once, then f(x) does not have an inverse.

So, from the options let's find a horizontal line (y = k) that intersects the graph more than once.

Drawing the horizontal lines, we have:

The line y = -4 intersects the graph in 2 points and thus proves that f(x) does not has an inverse function.

Answer: y = -4.