Chapter 23: Problem 33
Find the point(s) where the slope of a tangent line to the given curve has the given value. In Exercises \(35-38,\) solve the given problems. $$y=12 x-\frac{1}{3} x^{3} ; m_{\mathrm{tan}}=-4$$
Short Answer
Expert verified
Points: \((4, \frac{80}{3})\) and \((-4, -\frac{80}{3})\)."
Step by step solution
01
Find the Derivative
To find the slope of the tangent line to the curve, we need the derivative of the function. Given \( y = 12x - \frac{1}{3}x^3 \), the derivative \( y' \) is obtained using the power rule:\[\frac{dy}{dx} = 12 - x^2\]
02
Set Derivative Equal to Given Slope
The problem specifies that the slope of the tangent line should be \(-4\). Therefore, we set the derivative equal to \(-4\):\[12 - x^2 = -4\]
03
Solve for x
Solve the equation \( 12 - x^2 = -4 \) to find the values of \( x \):\[12 - x^2 = -4 \12 + 4 = x^2 \16 = x^2 \x = \pm 4\]
04
Find Corresponding y-values
Substitute \( x = 4 \) and \( x = -4 \) back into the original equation to find the corresponding \( y \)-values.For \( x = 4 \):\[y = 12(4) - \frac{1}{3}(4)^3 = 48 - \frac{1}{3}(64) = 48 - \frac{64}{3} = \frac{144}{3} - \frac{64}{3} = \frac{80}{3}\]For \( x = -4 \):\[y = 12(-4) - \frac{1}{3}(-4)^3 = -48 + \frac{1}{3}(64) = -48 + \frac{64}{3} = -\frac{144}{3} + \frac{64}{3} = -\frac{80}{3}\]
05
Conclusion
The coordinates of the point(s) on the curve where the slope of the tangent line is \(-4\) are \((4, \frac{80}{3})\) and \((-4, -\frac{80}{3})\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Derivative
The derivative of a function is a critical concept in calculus. It represents how a function changes or, in other words, the rate of change of the function's value with respect to changes in its input value. Imagine driving a car; the derivative tells you your speed at any given moment.
- In mathematical terms, the derivative of a function at a certain point is the slope of the tangent line to the curve at that point.
- To find a derivative, standard rules and techniques, like the power rule and product rule, are often applied.
Tangent Line
A tangent line is a straight line that just "touches" a curve at a given point without crossing it. Think of the tangent line as a mirror of the curve's behavior at a specific spot. Sometimes, a curve can resemble a rolling wave, with the tangent line at the peak of each wave showing the immediate direction of travel.
- The slope of the tangent line gives you a snapshot of the curve's steepness (or flatness) right there at the point of contact.
- This concept is crucial for understanding how graphs and models behave instantaneously, especially in real-world scenarios such as physics or economics.
Slope of a Curve
The slope of a curve at a particular point means the steepness of the line that is tangent to the curve at that point. Just like a mountain has varying inclines, a curve changes in steepness, and the slope gives a numerical value to that steepness.
- This slope is determined by the derivative: the derivative tells you how steep the curve is at any point.
- If the slope is positive, the curve is going upward; if it’s negative, the curve is going downward.
Power Rule
The Power Rule is a shorthand way of determining derivatives of polynomials. It states that if you have a term in the form of \[x^n\],its derivative is:\[nx^{n-1}\].In simpler terms, the power gets multiplied by the coefficient in front of \(x\), and then the power of \(x\) is reduced by one.
- This rule is especially useful in efficiently differentiating a wide variety of polynomial terms, saving time and effort.
- For example, for the function \(f(x) = x^3\), its derivative using the power rule is \(3x^2\).