The Limit — Question 10

Section 2-2 · Calculus pages 249–250

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Question 10

Evaluate the limit: limx→0sin⁡(3x)x\lim_{x \to 0} \frac{\sin(3x)}{x}

Question 10 - Solution

We are given: limx→0sin⁡(3x)x\lim_{x \to 0} \frac{\sin(3x)}{x}

We want to simplify the expression to match a known limit. Recall the standard limit: limu→0sin⁡(u)u=1\lim_{u \to 0} \frac{\sin(u)}{u} = 1

Let u=3xu = 3x. As x→0x \to 0, we also have u→0u \to 0.

So: sin⁡(3x)x=sin⁡(3x)3x⋅3\frac{\sin(3x)}{x} = \frac{\sin(3x)}{3x} \cdot 3

Now apply the limit: limx→0sin⁡(3x)x=limx→0(sin⁡(3x)3x⋅3)=(limu→0sin⁡(u)u)⋅3=1⋅3=3\lim_{x \to 0} \frac{\sin(3x)}{x} = \lim_{x \to 0} \left( \frac{\sin(3x)}{3x} \cdot 3 \right) = \left( \lim_{u \to 0} \frac{\sin(u)}{u} \right) \cdot 3 = 1 \cdot 3 = \boxed{3}