# Monday 7 April class

Topics:

• Exponential functions in applications where the rate of growth or decay (decrease) per unit time is known. (See Examples 15.6, 15.7, and 15.8)

Exponential growth and decay occur when the rate of change is a percentage of the quantity that is growing or decreasing. (Technically, we say that the rate of change is proportional to the quantity.)

If the rate of change r is known (as a percent per unit of time), then the base of the exponential function is $b = 1+r$ for exponential growth, or $b=1-r$ for exponential decay. In other words,

$f(t) = c(1+r)^t$ for exponential growth

$f(t) = c(1-r)^t$ for exponential decay

• Quick review of trigonometry (to be continued): See Session 17

Note: Better names for the two basic triangles are: the isosceles right triangle, and half of an equilateral triangle. These names are better for two reasons: first, they remind you of what the triangles are, and second, they are not tying you to the degree measure of the angles. (Remember, we are trying to learn to think in radians.)

Homework:

• Reread and review the examples from Session 15 that were discussed in class.

• Learn the two basic triangles for trigonometry. I recommend that you develop them from scratch the way that I did in class. Doing this a few times over a week or so will make them stay in your memory! Also practice thinking in radians, and review the material discussed in class.

• Finish the assigned problems from Session 15

• Do the assigned parts of Exercise 17.1

• No WeBWorK or Warm-Up this time, because of the test next time. Test 3 Review answers and discussion are over on the Piazza discussion board.

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