Math Problem Statement

1. The gradient of the tangent line to the graph of f(x) = 2x^2 + kx - 3 at x = 1 is 1.5. Find the value of k. 2. Write the equation of the tangent line to the graph of f(x) = x^3 ln(x) at x = 1.

Solution

Let's break down and solve each of the problems shown in the image.

Problem 1:

The gradient of the tangent line to the graph of f(x)=2x2+kx3f(x) = 2x^2 + kx - 3 at x=1x = 1 is 1.5. Find the value of kk.

To solve this, follow these steps:

  1. First, find the derivative of the function f(x)=2x2+kx3f(x) = 2x^2 + kx - 3. This will give us the slope of the tangent line at any point xx. f(x)=ddx(2x2+kx3)=4x+kf'(x) = \frac{d}{dx}(2x^2 + kx - 3) = 4x + k
  2. At x=1x = 1, the gradient (slope) is given as 1.5. Set f(1)=1.5f'(1) = 1.5: f(1)=4(1)+k=1.5f'(1) = 4(1) + k = 1.5 4+k=1.54 + k = 1.5 k=1.54=2.5k = 1.5 - 4 = -2.5 So, the value of kk is 2.5-2.5.

Problem 2:

Write the equation of the tangent line to the graph of f(x)=x3lnxf(x) = x^3 \ln x at x=1x = 1.

To solve this:

  1. Find the derivative of the function f(x)=x3lnxf(x) = x^3 \ln x using the product rule. Let u(x)=x3u(x) = x^3 and v(x)=lnxv(x) = \ln x, so the derivative is: f(x)=ddx(x3)lnx+x3ddx(lnx)f'(x) = \frac{d}{dx}(x^3) \cdot \ln x + x^3 \cdot \frac{d}{dx}(\ln x) f(x)=3x2lnx+x31xf'(x) = 3x^2 \ln x + x^3 \cdot \frac{1}{x} Simplifying: f(x)=3x2lnx+x2f'(x) = 3x^2 \ln x + x^2

  2. Evaluate this derivative at x=1x = 1: f(1)=3(1)2ln(1)+(1)2=0+1=1f'(1) = 3(1)^2 \ln(1) + (1)^2 = 0 + 1 = 1 So, the slope of the tangent line at x=1x = 1 is 1.

  3. To find the equation of the tangent line, we also need the function value at x=1x = 1: f(1)=(1)3ln(1)=10=0f(1) = (1)^3 \ln(1) = 1 \cdot 0 = 0

  4. The equation of the tangent line is given by the point-slope form: yf(1)=f(1)(x1)y - f(1) = f'(1)(x - 1) Substituting f(1)=0f(1) = 0 and f(1)=1f'(1) = 1: y0=1(x1)y - 0 = 1(x - 1) y=x1y = x - 1 Thus, the equation of the tangent line is y=x1y = x - 1.


Do you want further clarifications on any step or details?
Here are 5 related questions to practice:

  1. How would you find the tangent line equation if the function involved a different logarithmic or exponential term?
  2. What is the meaning of the gradient (slope) in the context of a tangent line to a curve?
  3. How does the value of kk in Problem 1 affect the shape of the parabola?
  4. What would the derivative of f(x)=xnlnxf(x) = x^n \ln x be for different powers of nn?
  5. How can you apply the chain rule when differentiating a composite function like (x2+1)lnx(x^2 + 1) \ln x?

Tip: When dealing with tangent lines, always find both the derivative at the point and the function value at that same point for accuracy.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Tangent Lines
Product Rule
Quadratic Equations

Formulas

f'(x) = 4x + k (derivative of 2x^2 + kx - 3)
f'(x) = 3x^2 ln(x) + x^2 (derivative of x^3 ln(x))
Point-slope form: y - y1 = m(x - x1)

Theorems

Derivative of a polynomial
Product rule for differentiation
Point-slope form of a line

Suitable Grade Level

Grade 11-12