Lesson 23

Comparing Functions

  • Let’s evaluate and compare functions.

23.1: Math Talk: Evaluating Functions

Mentally evaluate each of the functions when \(x = 3\).

\(f(x) = x^2 - 4x + 1\)

\(g(x) = 6x - 2x^2\)

\(h(x) = (x-4)(x-3)\)

\(j(x) = 2(x-1)(x+2)\)

23.2: Comparing Functions

The notation \(f(2)\) means the output of function \(f\) when \(x\) is 2. For each function, determine whether \(f(2) > f(3)\), \(f(2) < f(3)\), or \(f(2) = f(3)\).

  1. \(f(x) = x^2 + 2x+ 3\)
  2. \(f(x) = (x-2)(x-3)\)
  3. \(f(x) = \text{-}x^2 + 5\)
  4. Graph on coordinate plane.
  5. Graph of line on coordinate plane.
  6. Graph on coordinate plane. Horizontal axis by twos from negative 4 to 8. Vertical axis by twos from negative 4 to 8. Graph goes through point 0 comma 8.
  7. Graph of wiggly line on coordinate plane. Horizontal axis by twos from negative 4 to 8. Vertical axis by twos from negative 4 to 8. Graph goes through origin.

23.3: Finding the Vertex

Write each function in vertex form, then find the coordinates of the vertex.

  1. \(y = x^2 - 4x + 7\)
  2. \(y = (x-1)(x+3)\)
  3. \(y = (x-2)(x+2)\)
  4. \(y = x^2 - 2x + 1\)
  5. \(y = \text{-}x^2 -2x-6\)
  6. \(y = 2x^2 - 12x + 22\)
  7. Graph on coordinate plane. Horizontal axis by twos from negative 8 to 8. Vertical axis by twos from negative 4 to 8. Graph goes through point 0 comma 7.

Summary