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Left-hand limit at x = 2

Consider the piecewise function f(x)={3x+1x<2x2+3x≥2f(x) = \begin{cases} 3x+1 & x < 2 \\ x^2+3 & x \geq 2 \end{cases}

Evaluate lim⁡x→2−f(x)\displaystyle\lim_{x \to 2^-} f(x).

Hint

For xx approaching 2 from the left, values are slightly less than 2, so use the formula f(x)=3x+1f(x) = 3x+1 that applies for x<2x < 2.

Step-by-step solution

Since we are approaching x=2x=2 from the left, we consider values of xx slightly less than 2, such as 1.9,1.99,1.9991.9, 1.99, 1.999. For all such values, x<2x < 2, so we must use the rule f(x)=3x+1f(x) = 3x+1.

As x→2−x \to 2^-, we substitute into 3x+13x+1: the values approach 3(2)+1=73(2)+1 = 7. Therefore lim⁡x→2−f(x)=7\lim_{x\to 2^-} f(x) = 7.

Right-hand limit at x = 2

Evaluate lim⁡x→2+f(x)\displaystyle\lim_{x \to 2^+} f(x).

Hint

For xx approaching 2 from the right, values are slightly greater than or equal to 2, so use the formula f(x)=x2+3f(x) = x^2+3 that applies for x≥2x \geq 2.

Step-by-step solution

Since we are approaching x=2x=2 from the right, we consider values of xx slightly greater than 2, such as 2.1,2.01,2.0012.1, 2.01, 2.001. For all such values, x≥2x \geq 2, so we must use the rule f(x)=x2+3f(x) = x^2+3.

As x→2+x \to 2^+, we substitute into x2+3x^2+3: the values approach (2)2+3=7(2)^2+3 = 7. Wait — let's recompute carefully: 22+3=4+3=72^2 + 3 = 4+3 = 7. So lim⁡x→2+f(x)=7\lim_{x\to 2^+} f(x) = 7.

Existence of the two-sided limit

Based on your results from the one-sided limits, does lim⁡x→2f(x)\displaystyle\lim_{x \to 2} f(x) exist? If it exists, state its value.

Hint

Recall that a two-sided limit exists if and only if the left-hand and right-hand limits both exist and are equal.

Step-by-step solution

From part (a), lim⁡x→2−f(x)=7\lim_{x\to 2^-} f(x) = 7, and from part (b), lim⁡x→2+f(x)=7\lim_{x\to 2^+} f(x) = 7. Since both one-sided limits exist and are equal to the same value.

the two-sided limit exists and equals that common value: lim⁡x→2f(x)=7\lim_{x\to 2} f(x) = 7.

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