Math Problem Statement

  1. Given f(x) = 2x 2 − x + 2, use the limit definition m = lim h→0 f(a + h) − f(a) h or limx→a f(x) − f(a) x − a to find the slope of the tangent line to the curve at x = 2. Use your result to write an equation of the tangent line at x = 2

Solution

We are asked to find the slope of the tangent line to the curve f(x)=2x2x+2f(x) = 2x^2 - x + 2 at x=2x = 2, and then use that result to write the equation of the tangent line. To do this, we'll use the limit definition of the derivative:

m=limh0f(a+h)f(a)hm = \lim_{h \to 0} \frac{f(a + h) - f(a)}{h}

where a=2a = 2. Let's break this process into steps.

Step 1: Compute f(a+h)f(a + h)

First, substitute x=a+hx = a + h into f(x)f(x). Here, a=2a = 2, so we find f(2+h)f(2 + h):

f(2+h)=2(2+h)2(2+h)+2f(2 + h) = 2(2 + h)^2 - (2 + h) + 2

Simplifying the right-hand side:

=2(4+4h+h2)(2+h)+2= 2(4 + 4h + h^2) - (2 + h) + 2 =2(4+4h+h2)2h+2= 2(4 + 4h + h^2) - 2 - h + 2 =8+8h+2h22h+2= 8 + 8h + 2h^2 - 2 - h + 2 =8h+2h2+82h+2= 8h + 2h^2 + 8 - 2 - h + 2 =2h2+7h+8= 2h^2 + 7h + 8

So, f(2+h)=2h2+7h+8f(2 + h) = 2h^2 + 7h + 8.

Step 2: Compute f(a)f(a)

Next, compute f(2)f(2):

f(2)=2(2)22+2=82+2=8f(2) = 2(2)^2 - 2 + 2 = 8 - 2 + 2 = 8

Step 3: Apply the limit definition of the derivative

Now, substitute f(2+h)f(2 + h) and f(2)f(2) into the limit definition:

m=limh0f(2+h)f(2)hm = \lim_{h \to 0} \frac{f(2 + h) - f(2)}{h} =limh0(2h2+7h+8)8h= \lim_{h \to 0} \frac{(2h^2 + 7h + 8) - 8}{h} =limh02h2+7hh= \lim_{h \to 0} \frac{2h^2 + 7h}{h} =limh0(2h+7)= \lim_{h \to 0} (2h + 7)

As h0h \to 0, the expression becomes:

m=7m = 7

So, the slope of the tangent line at x=2x = 2 is 77.

Step 4: Write the equation of the tangent line

To find the equation of the tangent line, we use the point-slope form of a line:

yy1=m(xx1)y - y_1 = m(x - x_1)

Here, m=7m = 7, x1=2x_1 = 2, and y1=f(2)=8y_1 = f(2) = 8. Substituting these values:

y8=7(x2)y - 8 = 7(x - 2)

Simplifying:

y8=7x14y - 8 = 7x - 14 y=7x6y = 7x - 6

Thus, the equation of the tangent line at x=2x = 2 is:

y=7x6y = 7x - 6

Would you like a detailed breakdown of any part, or any clarifications?

Here are 5 related questions for further practice:

  1. How would you find the slope of the tangent line for f(x)=3x24x+1f(x) = 3x^2 - 4x + 1 at x=1x = 1?
  2. What does the derivative of a function tell us geometrically?
  3. Can you find the derivative of f(x)=x32x+5f(x) = x^3 - 2x + 5 using the limit definition?
  4. How would the tangent line at x=0x = 0 differ from the one at x=2x = 2 for the same function?
  5. How do the limits in calculus relate to the concept of continuity?

Tip: When finding the equation of a tangent line, always double-check both the slope and the point of tangency, as these are critical in the point-slope form of the line.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Limits
Tangent Line

Formulas

Limit definition of the derivative: m = lim h→0 [f(a+h) − f(a)] / h
Point-slope form of a line: y − y₁ = m(x − x₁)

Theorems

Derivative as the slope of the tangent line

Suitable Grade Level

Grades 11-12