# Lesson 2

Understanding Points in Situations

• Let’s understand points on a function in a situation.

### 2.1: A Day of Temperature

The temperature for a city is a function of time after midnight. The graph shows the values on a particular spring day.

1. What does the point on the graph where $$x = 15$$ mean?
2. What is the temperature at 5 p.m.?
3. What is the hottest it gets on this day?
4. What is the coldest it gets on this day?

### 2.2: What Happens to -2?

For each of these equations, find the value of $$y$$ when $$x = \text{-}2$$.

1. $$y = 3x - 4$$
2. $$y = 10 - 2x$$
3. $$y = \frac{3}{2}x + 5$$
4. $$y = 2(x - 1) + 4$$
5. $$y = \text{-}x + 19$$
6. $$y = \frac{x - 3}{8}$$
7. $$y = 0.3x + 5$$

### 2.3: It’s Heating Up!

The temperature, in degrees Fahrenheit, of a scientific sample being warmed steadily as a function of time in seconds after the sample is put in a machine can be represented by the equation $$y = 2.1x + 86$$.

1. What does it mean when $$x = 2$$?
2. What is the temperature in that situation?
3. What does it mean when $$y = 122$$?
4. A graph of this equation goes through the point $$(60,212)$$. What does that mean?
5. Give 2 values for $$x$$ that do not make sense. Explain your reasoning.
6. Give 2 values for $$y$$ that do not make sense. Explain your reasoning.