Math Problem Statement

Find the equation of the tangent line to the graph of y = ln(5 - x^2) at x = 2.

Solution

To find the equation of the tangent line to the graph of y=ln(5x2)y = \ln(5 - x^2) at x=2x = 2, we can follow these steps:

Step 1: Differentiate the function

The general form of the equation for the tangent line is: yy1=m(xx1)y - y_1 = m(x - x_1) where mm is the slope of the tangent line, and (x1,y1)(x_1, y_1) is the point of tangency. To find mm, we need the derivative of yy.

The function given is: y=ln(5x2)y = \ln(5 - x^2)

Using the chain rule for derivatives, we get: dydx=15x2ddx(5x2)\frac{dy}{dx} = \frac{1}{5 - x^2} \cdot \frac{d}{dx}(5 - x^2) The derivative of 5x25 - x^2 is 2x-2x, so: dydx=2x5x2\frac{dy}{dx} = \frac{-2x}{5 - x^2}

Step 2: Evaluate the derivative at x=2x = 2

Now, substitute x=2x = 2 into the derivative to find the slope mm: dydxx=2=2(2)522=454=41=4\frac{dy}{dx}\bigg|_{x = 2} = \frac{-2(2)}{5 - 2^2} = \frac{-4}{5 - 4} = \frac{-4}{1} = -4 Thus, the slope of the tangent line is m=4m = -4.

Step 3: Find the point of tangency

Next, find the yy-coordinate of the point of tangency by substituting x=2x = 2 into the original function: y=ln(522)=ln(54)=ln(1)=0y = \ln(5 - 2^2) = \ln(5 - 4) = \ln(1) = 0 So, the point of tangency is (2,0)(2, 0).

Step 4: Write the equation of the tangent line

Using the point-slope form of the equation of a line: yy1=m(xx1)y - y_1 = m(x - x_1) Substitute y1=0y_1 = 0, m=4m = -4, and x1=2x_1 = 2: y0=4(x2)y - 0 = -4(x - 2) y=4(x2)y = -4(x - 2)

Final Answer:

The equation of the tangent line is: y=4(x2)y = -4(x - 2)

Would you like further details or explanations? Here are some related questions for practice:

  1. What is the significance of the derivative in determining the slope of a tangent line?
  2. How does the chain rule apply when differentiating composite functions like ln(5x2)\ln(5 - x^2)?
  3. What is the meaning of the point-slope form of a line equation?
  4. Can you find the tangent line at a different point, say x=1x = 1, for the same function?
  5. What happens to the tangent line if x=0x = 0? Does the tangent exist there?

Tip: Always check that the argument inside a logarithmic function is positive before evaluating!

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Tangent Line
Logarithmic Differentiation

Formulas

y - y_1 = m(x - x_1)
Derivative of ln(u) is (1/u) * du/dx
Slope of tangent line = dy/dx

Theorems

Chain Rule
Derivative of Logarithmic Functions

Suitable Grade Level

Grades 11-12 or College-level Calculus