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Limits

Here is the expression sin (x)/x.
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If you replace x by 0, the expression becomes 0/0, and you get an indeterminate result.
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If you find the numerical value of sin (x)/x for x close to 0, however, you get a result that is close to 1.
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This finds the limit of sin (x)/x as x approaches 0. The result is indeed 1.
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Limit[expr,x->x0]the limit of expr as x approaches x0

Limits.