December 4, 2012Finding the slope and y-intercept of the line to write an equation

Warm-up:1. If f(x) = -4x + 5, find a) f(-8) and b) f(-2x – 3)

2. Write an equation for the following situation: A gym membership has an initial fee of $100 and a monthly fee of $25. Let x represent the months and y, the amount spent on the membership.

Two forms of a line:Slope Intercept Form and Function Form

What we called it before: y = rate(x) + base

Slope Intercept Form: y = mx + b

Function Form: f(x) = mx + b

Let’s look at the graphs and equations from HW 4.8

We can now identify the slope and y-intercept from a graph.y = mx + b

(pick 2 points on the graph)

y-intercept (base): when x = 0 and hits the y-axis

Identify the slope and y-intercept, then write the equation: y = mx + b

Positive slope Negative slope

What is the slope and equation for horizontal and vertical lines?

Finding the slope between two points

• You only need two points to find the slope of a line.Find the slope between (5, 1) and (2, -3).

Using a tableUsing a formula

Try one more using any strategy: Find the slope between (2, 3) and (2, -3)