WEBVTT

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Here is the problem: sin(4x)/(2x).

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Find the limit of sin(4 x) / (2 x) as x → 0.

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Indeterminate form 0 over 0 — apply L prime Hôpital prime s rule. Differentiate the numerator and the denominator separately (this is not the quotient rule).

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Simplify.

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Direct substitution. The expression is continuous at x equals 0, so the limit equals its value there.

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So the answer is Limit equals 2.

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A limit describes the value a function approaches, not necessarily the value it takes. When substitution gives an indeterminate form, the expression is rewritten (L prime Hôpital prime s rule, a conjugate, or logarithms) until substitution works.

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Numerical values from the right agree: f(0.01) equals 1.9994667, f(0.001) equals 1.9999947, f(0.0001) equals 1.9999999, f(0.00001) equals 2, which checks out.

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Numerical values from the left agree: f(negative 0.01) equals 1.9994667, f(negative 0.001) equals 1.9999947, f(negative 0.0001) equals 1.9999999, f(negative 0.00001) equals 2, which checks out.