Question

The graph of y=f(x) is given above. For what value of x is y=f(x-4) undefined?

Answer 1

Answer: Choice D) 5

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Notice the hole at (1,2). This means x = 1 and y = 2
y = f(x)
y = f(1) after we replace x with 1
y = 2

If we go from f(x) to f(x-4), then we shift the xy axis four units to the left. The curve will stay still though it will move relative to the xy axis. The xy axis moves four units to the left, so it appears that the curve moved 4 units to the right.

Add 4 to the x coordinate:
x = 1 ---> x+4 = 1+4 = 5
The y coordinate stays the same. No vertical shifting is done.

So we go from (1,2) to (5,2)
(1,2) is a hole on y = f(x)
(5,2) is a hole on y = f(x-4)

This is why the answer is x = 5