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Squeeze theorem applied to x^2 + x sin(1/x)

Consider the function g(x)=x2+xsin⁡(1x)g(x) = x^2 + x\sin\left(\frac{1}{x}\right) for x≠0x \neq 0. Note that direct substitution fails at x=0x=0 since sin⁡(1/x)\sin(1/x) is undefined there and oscillates wildly nearby. Use the fact that −1≤sin⁡(1/x)≤1-1 \le \sin(1/x) \le 1 for all x≠0x \neq 0 to construct upper and lower bounding functions for g(x)g(x), and apply the Squeeze Theorem to evaluate lim⁡x→0(x2+xsin⁡(1x)).\lim_{x \to 0} \left(x^2 + x\sin\left(\frac{1}{x}\right)\right). State the value of this limit.

Hint

Start from −1≤sin⁡(1/x)≤1-1 \le \sin(1/x) \le 1, multiply through by xx (being careful this reverses inequalities when x<0x<0, but you can instead bound xsin⁡(1/x)x\sin(1/x) using −∣x∣≤xsin⁡(1/x)≤∣x∣-|x|\le x\sin(1/x)\le |x|), then add x2x^2 to all sides and take the limit of the outer bounds.

Step-by-step solution

Since −1≤sin⁡(1/x)≤1-1 \le \sin(1/x) \le 1 for all x≠0x \neq 0, multiplying by ∣x∣|x| gives −∣x∣≤xsin⁡(1/x)≤∣x∣-|x| \le x\sin(1/x) \le |x|, which holds for both positive and negative xx. Adding x2x^2 to every part of this inequality yields x2−∣x∣≤g(x)≤x2+∣x∣x^2 - |x| \le g(x) \le x^2 + |x|, giving valid squeezing bounds near x=0x=0.

Now take the limit of the outer expressions as x→0x \to 0: both x2−∣x∣x^2 - |x| and x2+∣x∣x^2 + |x| approach 0−0=00 - 0 = 0 by direct substitution, since these are continuous functions. Because g(x)g(x) is squeezed between two functions that both tend to 00, the Squeeze Theorem guarantees lim⁡x→0g(x)=0\lim_{x\to 0} g(x) = 0.

Behavior of the bounding functions near zero

Hint
Step-by-step solution

Both bounding functions, x squared minus the absolute value of x and x squared plus the absolute value of x, approach zero as x approaches zero. This shared value is exactly what forces the squeezed function g of x to also approach zero. The answer is zero.

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