Module 6: Exponents and Logarithms

 

tip
Remember that when you sketch a graph, you must apply the transformations in the order of stretches and reflections before translations.

In Try This 4 you may have found that the parameters a, b, h, and k change the graph of an exponential function in the form f(x) = a(c)b(xh) + k in the ways summarized in the following chart. Note: You may find it helpful to look at Multiple Transformations from Try This 4 as you review this chart.

 

Parameter

Transformation

Example

 

a

  • vertical stretch by a factor of |a| about the x-axis
  • when a < 0, reflection in the x-axis
  • mapping notation: (x, y) → (x, ay)
This is a graph of 3 exponential functions. Their equations are y equals 3 times 2 to the power x, y equals 2 to the power x, and y equals negative 2 times 2 to the power x. The two graphs with positive coefficients rise to the right and the graph with a negative coefficient falls to the right.

 

b

  • horizontal stretch by a factor of   about the y-axis
  • when b < 0, reflection in the y-axis
  • mapping notation:
This is a graph of 3 exponential functions. Their equations are y equals 2 to the power negative 2 times x, y equals 2 to the power x, and y equals 2 to the power x divided by 3. The two graphs with positive powers rise to the right from the second quadrant to the first quadrant. The graph with a negative power rises from the first quadrant to the second quadrant.

 

h

  • horizontal translation of h units left or right
  • mapping notation: (x, y) → (x + h, y)
This is a graph of 3 exponential functions. Their equations are y equals 2 to the power x plus 3, y equals 2 to the power x, and y equals 2 to the power x minus 2. All graphs rise to the right from the second quadrant to the first quadrant.

 

k

  • vertical translation of k units up or down
  • mapping notation: (x, y) → (x, y + k)
This is a graph of 3 exponential functions. Their equations are y equals 2 to the power x and then 3 is added, y equals 2 to the power x, and y equals 2 to the power x and then 2 is subtracted.