Math Problem Statement

For what value of the constant c is the function f continuous on (-∞, ∞)? The function f(x) is given by: f(x) = cx^2 + 3x if x < 2, and f(x) = x^3 - cx if x ≥ 2. The function is continuous on (-∞, 2) and (2, ∞). To ensure continuity on (-∞, ∞), we need to check the limits as x approaches 2 from both sides.

Solution

To solve this problem, we need to ensure the function f(x)f(x) is continuous at x=2x = 2. Continuity at x=2x = 2 requires that the left-hand limit and right-hand limit of f(x)f(x) as xx approaches 2 are equal, and that they also equal the function's value at x=2x = 2.

Given the piecewise function:

cx^2 + 3x & \text{if } x < 2 \\ x^3 - cx & \text{if } x \geq 2 \end{cases}$$ ### Step 1: Find the Left-Hand Limit as $$x \to 2^-$$ The left-hand limit as $$x$$ approaches 2 from the left is: $$\lim_{x \to 2^-} f(x) = \lim_{x \to 2^-} (cx^2 + 3x)$$ Substitute $$x = 2$$ into the equation: $$\lim_{x \to 2^-} f(x) = c(2)^2 + 3(2) = 4c + 6$$ ### Step 2: Find the Right-Hand Limit as $$x \to 2^+$$ The right-hand limit as $$x$$ approaches 2 from the right is: $$\lim_{x \to 2^+} f(x) = \lim_{x \to 2^+} (x^3 - cx)$$ Substitute $$x = 2$$ into the equation: $$\lim_{x \to 2^+} f(x) = (2)^3 - c(2) = 8 - 2c$$ ### Step 3: Set the Limits Equal for Continuity For the function to be continuous at $$x = 2$$, the left-hand limit and right-hand limit must be equal: $$4c + 6 = 8 - 2c$$ Now, solve for $$c$$: $$4c + 2c = 8 - 6$$ $$6c = 2$$ $$c = \frac{1}{3}$$ So, the value of the constant $$c$$ that makes the function continuous on $$(-\infty, \infty)$$ is $$c = \frac{1}{3}$$. If you have any further questions or need more details, feel free to ask! --- ### Related Questions: 1. How does the value of $$c$$ affect the shape of the graph for $$x < 2$$ and $$x \geq 2$$? 2. What happens to the function if $$c$$ is not equal to $$\frac{1}{3}$$? 3. How do you check for differentiability at $$x = 2$$? 4. Can the function be discontinuous at any other point besides $$x = 2$$? 5. How would you find the derivative of the function for both intervals? ### Tip: Always remember to check both the left-hand and right-hand limits when verifying continuity at a particular point in a piecewise function.

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Math Problem Analysis

Mathematical Concepts

Continuity
Piecewise Functions
Limits

Formulas

Left-hand limit: lim(x → 2-) f(x) = lim(x → 2-) (cx^2 + 3x)
Right-hand limit: lim(x → 2+) f(x) = lim(x → 2+) (x^3 - cx)

Theorems

Continuity at a point theorem

Suitable Grade Level

Grades 10-12