# Identifying slope from equation

Lesson

Let's have a quick recap of what we know about straight lines on the Cartesian plane so far.

• They have a slope (slope), a measure of how steep the line is.
• They can be increasing (positive slope) or decreasing (negative slope).
• They can be horizontal (zero slope).
• They can be vertical (slope is undefined).
• They have $x$x intercepts, $y$y intercepts or both an $x$x and a $y$y intercept.
• The slope can be calculated using $\frac{\text{rise }}{\text{run }}$rise run or $\frac{y_2-y_1}{x_2-x_1}$y2y1x2x1.
• They have an equation of the form $y=mx+b$y=mx+b.

The values of $m$m and $b$b mean specific things. Explore for yourself what these values do by exploring on this interactive.

## Slope

So what you will have found is that the $m$m value affects the slope.

• If $m<0$m<0, the slope is negative and the line is decreasing
• if $m>0$m>0, the slope is positive and the line is increasing
• if $m=0$m=0 the slope is $0$0 and the line is horizontal
• Also, the larger the value of $m$m the steeper the line

## Y-Intercept

We also found that the $b$b value affects the $y$y intercept.

• If $b$b is positive then the line is vertically translated (moved) up.
• If $b$b is negative then the line is vertically translated (moved) down.
##### Question 1

$y=3x$y=3x

a) What is the the slope?  The slope is the value of the coefficient, (the number in front of the $x$x).

The slope of this line is 3.

b) What is the $y$y-intercept?  The $y$y-intercept is the value of the constant term, (the number on its own).  The $y$y-intercept of this line is 0.

##### Question 2

$y=-2x$y=2x

• slope is $-2$2
• $y$y intercept is $0$0

##### Question 3

$y=\frac{x}{2}-3$y=x23

• slope is $\frac{1}{2}$12
• $y$y intercept is $-3$3

##### Question 4

Consider the equation $y=-1-\frac{9x}{2}$y=19x2.

1. State the slope of the line.

2. State the $y$y-value of the $y$y-intercept.

##### Question 5

$2y=-4x+10$2y=4x+10

First we need to rewrite it in the form or $y=mx+b$y=mx+b.

$y=-2x+5$y=2x+5

• slope is $-2$2
• $y$y intercept is $5$5

### Outcomes

#### 10P.LR2.02

Identify, through investigation, y = mx + b as a common form for the equation of a straight line, and identify the special cases x = a, y = b;

#### 10P.LR2.03

Identify, through investigation with technology, the geometric significance of m and b in the equation y=mx + b