Mathematics

Mathematics

Problem

In one or two sentences, explain why lim⁡x→0sin⁡xx\displaystyle \lim_{x\to 0}\frac{\sin x}{x} equals 11 only when xx is measured in radians rather than degrees.
Intuitive explanation

The sine function's Taylor series sin⁡x=x−x33!+⋯\sin x = x - \frac{x^3}{3!} + \cdots is derived assuming xx is in radians, so sin⁡xx→1\frac{\sin x}{x} \to 1 as x→0x \to 0. If xx were in degrees, you'd need a conversion factor: sin⁡(x°)=sin⁡(πx180)\sin(x°) = \sin\left(\frac{\pi x}{180}\right), which introduces π180\frac{\pi}{180} into the limit and changes the answer to π180\frac{\pi}{180} instead of 11.

Intuitive explanation

The sine function's Taylor series sin⁡x=x−x33!+⋯\sin x = x - \frac{x^3}{3!} + \cdots is derived assuming xx is in radians, so sin⁡xx→1\frac{\sin x}{x} \to 1 as x→0x \to 0. If xx were in degrees, you'd need a conversion factor: sin⁡(x°)=sin⁡(πx180)\sin(x°) = \sin\left(\frac{\pi x}{180}\right), which introduces π180\frac{\pi}{180} into the limit and changes the answer to π180\frac{\pi}{180} instead of 11.

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