Math Problem Statement

Consider the following: f(x) = -5/2x^2 + 8x + 8. Find f'(x), f'(-1), and the slope and equation of the tangent line to the graph of the function f at the point (-1, -5/2).

Solution

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Given Function:

f(x)=52x2+8x+8f(x) = -\frac{5}{2}x^2 + 8x + 8

1. Find f(x)f'(x) (the derivative of f(x)f(x)):

We differentiate the function term by term: f(x)=ddx(52x2+8x+8)f'(x) = \frac{d}{dx}\left( -\frac{5}{2}x^2 + 8x + 8 \right)

  • The derivative of 52x2-\frac{5}{2}x^2 is 5x-5x (using the power rule).
  • The derivative of 8x8x is 88.
  • The derivative of the constant 88 is 00.

Thus, f(x)=5x+8f'(x) = -5x + 8

2. Find f(1)f'(-1):

Substitute x=1x = -1 into f(x)f'(x): f(1)=5(1)+8=5+8=13f'(-1) = -5(-1) + 8 = 5 + 8 = 13

3. Find the slope and equation of the tangent line at (1,52)(-1, -\frac{5}{2}):

  • The slope of the tangent line is given by f(1)f'(-1), which we calculated to be 13.

Next, we find the equation of the tangent line using the point-slope form of a line: yy1=m(xx1)y - y_1 = m(x - x_1) Where:

  • m=13m = 13 (the slope),
  • (x1,y1)=(1,52)(x_1, y_1) = \left(-1, -\frac{5}{2}\right) (the given point on the graph).

Substitute the values: y(52)=13(x(1))y - \left(-\frac{5}{2}\right) = 13(x - (-1)) Simplify: y+52=13(x+1)y + \frac{5}{2} = 13(x + 1) y+52=13x+13y + \frac{5}{2} = 13x + 13 Now subtract 52\frac{5}{2} from both sides to get the equation in slope-intercept form: y=13x+1352y = 13x + 13 - \frac{5}{2} Convert 1313 to a fraction: y=13x+26252y = 13x + \frac{26}{2} - \frac{5}{2} y=13x+212y = 13x + \frac{21}{2} Thus, the equation of the tangent line is: y=13x+212y = 13x + \frac{21}{2}

Final Answers:

  1. f(x)=5x+8f'(x) = -5x + 8
  2. f(1)=13f'(-1) = 13
  3. Slope = 13, Equation of tangent line: y=13x+212y = 13x + \frac{21}{2}

Would you like any further details or explanations?

Here are 5 related questions for practice:

  1. What is the second derivative f(x)f''(x) for the given function?
  2. How do you find the critical points of f(x)f(x)?
  3. What is the concavity of f(x)f(x) at x=1x = -1?
  4. How does the equation of the normal line at the point (1,52)(-1, -\frac{5}{2}) differ from the tangent line?
  5. What is the vertex of the parabola represented by f(x)f(x)?

Tip: The tangent line at any point on a curve has the same slope as the derivative of the function at that point.

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Math Problem Analysis

Mathematical Concepts

Calculus
Derivatives
Tangent Lines
Quadratic Functions

Formulas

Derivative of a function: f'(x) = d/dx [f(x)]
Power Rule: d/dx [x^n] = n*x^(n-1)
Point-slope form of a line: y - y1 = m(x - x1)

Theorems

Differentiation rules
Tangent line to a curve is given by the derivative at a point

Suitable Grade Level

Grades 11-12, Calculus I