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Find an equation for the tangent line to the curve at the given point. Then sketch the curve and tangent line together. \( y=-4 x^{3},(-1,4) \) An equation for the tangent line is (Type an equation.)

Ask by Schwartz Clarke. in the United States
Mar 09,2025

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Tutor-Verified Answer

Answer

An equation for the tangent line is \( y = -12x - 8 \).

Solution

1. Differentiate the function with respect to \( x \). Since \( y = -4x^3 \), the derivative is \[ \frac{dy}{dx} = -4 \cdot 3x^2 = -12x^2. \] 2. Evaluate the derivative at the given point \( x = -1 \) to find the slope of the tangent line. \[ m = -12(-1)^2 = -12 \cdot 1 = -12. \] 3. Use the point-slope form of a line with the point \( (-1, 4) \) and slope \( m = -12 \). The point-slope form of a line is given by \[ y - y_1 = m(x - x_1). \] Substitute \( x_1 = -1 \), \( y_1 = 4 \), and \( m = -12 \) into the formula: \[ y - 4 = -12(x - (-1)) = -12(x + 1). \] 4. Solve for \( y \) to write the equation in slope-intercept form: \[ y - 4 = -12x - 12. \] Adding 4 to both sides: \[ y = -12x - 12 + 4, \] \[ y = -12x - 8. \] Thus, an equation for the tangent line is \[ y = -12x - 8. \]

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Bonus Knowledge

To find the equation for the tangent line to the curve \( y = -4x^3 \) at the point \((-1, 4)\), we first need to calculate the derivative of the function to find the slope at that point. The derivative is: \[ \frac{dy}{dx} = -12x^2 \] Now, substitute \( x = -1 \): \[ \frac{dy}{dx} \bigg|_{x=-1} = -12(-1)^2 = -12 \] The slope of the tangent line at the point \((-1, 4)\) is \(-12\). We can use the point-slope form of the line equation \( y - y_1 = m(x - x_1) \): \[ y - 4 = -12(x + 1) \] Simplifying this gives: \[ y = -12x - 12 + 4 \] \[ y = -12x - 8 \] So the equation for the tangent line is: \[ y = -12x - 8 \] Happy sketching! You’ll see the curve \( y = -4x^3 \) drops steeply in both directions, while the tangent line slopes sharply downward, creating a striking visual contrast at the point \((-1, 4)\).

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