Question

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Answer 1

The invisible lines are called asymptotes.
Mainly there are two asymptotes: horizontal and vertical.
For example the function f(x) = 1 / (x-3) has a vertical asymptote at x = 3.
Since the the denominator can never be zero, x can never be 3. But x can get really, really close to 3 from either side but it can never get to 3. Examples: 2.9999999 and 3.0000001.
The y value will get very large as x approaches 3. And x = 3 is the invisible line that the graph won't cross. This is a vertical asymptote.

There is horizontal asymptote too.

Answer 2

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