How can I explain each function is discontinous at given point.

f(x) x^2 - 1 / over x + 1

at x = -1

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________( x^2 -1 / over x +1, if x doesn't equal -1

F(x)= ___(

________( 6, if x = -1

It should be a big parenthesis but i couldn't draw it here, so i put three (