Understanding the Function and Its Derivative

Oct 13, 2025 by wbrum.org 52 views

Introduction

In calculus, finding the equation of a tangent line to a function at a given point is a fundamental concept. It involves using the derivative of the function to determine the slope of the tangent line and then using the point-slope form of a line to write the equation of the tangent line. In this article, we will explore how to find the equation of the tangent line to the graph of the cubic function $$f(x) = -x^3 + 4x - 2$$ at the point $$x = -2$$.

Understanding the Function and Its Derivative

The given function is a cubic function, which means it has a term with a degree of 3. The function is $$f(x) = -x^3 + 4x - 2$$. To find the equation of the tangent line, we need to find the derivative of the function, which represents the slope of the tangent line.

To find the derivative of the function, we will use the power rule of differentiation, which states that if $$f(x) = x^n$$, then $$f'(x) = nx^{n-1}$$. We will apply this rule to each term in the function.

The derivative of $$-x^3$$ is $$-3x^2$$.

The derivative of $$4x$$ is $$4$$.

The derivative of $$-2$$ is $$0$$, since the derivative of a constant is always $$0$$.

Therefore, the derivative of the function is $$f'(x) = -3x^2 + 4$$.

Finding the Slope of the Tangent Line

Now that we have the derivative of the function, we can find the slope of the tangent line at the point $$x = -2$$. To do this, we will substitute $$x = -2$$ into the derivative.

f'(-2) = -3(-2)^2 + 4

f'(-2) = -3(4) + 4

f'(-2) = -12 + 4

f'(-2) = -8

Therefore, the slope of the tangent line at the point $$x = -2$$ is $$-8$$.

Finding the Equation of the Tangent Line

Now that we have the slope of the tangent line, we can find the equation of the tangent line using the point-slope form of a line. The point-slope form is given by:

y - y_1 = m(x - x_1)

where $$m$$ is the slope of the line, and $$(x_1, y_1)$$ is a point on the line.

In this case, we know that the slope of the tangent line is $$-8$$, and we want to find the equation of the tangent line at the point $$x = -2$$. To do this, we need to find the value of $$y_1$$, which is the value of the function at $$x = -2$$.

y_1 = f(-2)

y_1 = -(-2)^3 + 4(-2) - 2

y_1 = -(-8) - 8 - 2

y_1 = 8 - 8 - 2

y_1 = -2

Therefore, the point $$(x_1, y_1)$$ is $$(-2, -2)$$.

Now we can substitute the values of $$m$$, $$x_1$$, and $$y_1$$ into the point-slope form of a line.

y - (-2) = -8(x - (-2))

y + 2 = -8(x + 2)

y + 2 = -8x - 16

y = -8x - 18

Therefore, the equation of the tangent line to the graph of $$f(x) = -x^3 + 4x - 2$$ at the point $$x = -2$$ is $$y = -8x - 18$$.

Conclusion

In this article, we have shown how to find the equation of the tangent line to the graph of a cubic function at a given point. We used the derivative of the function to determine the slope of the tangent line and then used the point-slope form of a line to write the equation of the tangent line. We found that the equation of the tangent line to the graph of $$f(x) = -x^3 + 4x - 2$$ at the point $$x = -2$$ is $$y = -8x - 18$$.

Introduction

In our previous article, we explored how to find the equation of the tangent line to the graph of a cubic function at a given point. We used the derivative of the function to determine the slope of the tangent line and then used the point-slope form of a line to write the equation of the tangent line. In this article, we will answer some common questions related to finding the equation of a tangent line to a cubic function.

Q: What is the derivative of a cubic function?

A: The derivative of a cubic function is a quadratic function. To find the derivative of a cubic function, we will use the power rule of differentiation, which states that if $$f(x) = x^n$$, then $$f'(x) = nx^{n-1}$$. We will apply this rule to each term in the function.

Q: How do I find the slope of the tangent line to a cubic function?

A: To find the slope of the tangent line to a cubic function, we will substitute the given point into the derivative of the function. The derivative of the function represents the slope of the tangent line.

Q: What is the point-slope form of a line?

A: The point-slope form of a line is given by:

y - y_1 = m(x - x_1)

where $$m$$ is the slope of the line, and $$(x_1, y_1)$$ is a point on the line.

Q: How do I find the equation of the tangent line to a cubic function?

A: To find the equation of the tangent line to a cubic function, we will use the point-slope form of a line. We will substitute the values of $$m$$, $$x_1$$, and $$y_1$$ into the point-slope form of a line.

Q: What is the equation of the tangent line to the graph of $$f(x) = -x^3 + 4x - 2$$ at the point $$x = -2$$?

A: The equation of the tangent line to the graph of $$f(x) = -x^3 + 4x - 2$$ at the point $$x = -2$$ is $$y = -8x - 18$$.

Q: How do I know if the tangent line is parallel to the x-axis or the y-axis?

A: If the slope of the tangent line is $$0$$, then the tangent line is parallel to the x-axis. If the slope of the tangent line is undefined, then the tangent line is parallel to the y-axis.

Q: Can I find the equation of the tangent line to a cubic function using other methods?

A: Yes, you can find the equation of the tangent line to a cubic function using other methods, such as implicit differentiation or the chain rule. However, the method we used in this article is the most straightforward and easiest to understand.

Q: What is the significance of finding the equation of the tangent line to a cubic function?

A: Finding the equation of the tangent line to a cubic function is important in many areas of mathematics and science, such as physics, engineering, and economics. It helps us understand the behavior of the function and make predictions about its future values.

Conclusion

In this article, we have answered some common questions related to finding the equation of a tangent line to a cubic function. We have shown how to find the derivative of a cubic function, the slope of the tangent line, and the equation of the tangent line. We have also discussed the significance of finding the equation of the tangent line to a cubic function.