Anthracene tends to be positive and negative in mathematics, which is expressed in mathematical language as follows: X tends to be (x0)+, or X tends to be (x0)-(x0 is a real number). Generally, it appears when seeking the limit, and X tends to (x0)+, which means that X approaches (x0) from the side (the right side of x0) greater than (x0), which means seeking the right limit at x0; Similarly, x tends to (x0)-, which means that x approaches (x0) from the side less than (x0) (the left side of x0), which means that the left limit is found at x0.

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