6/06/2010 @ 2:05 PM
Linear Relations
In this unit, you will learn about slope, slope as a rate of change, direct variation, and partial variation.First, we learned about slope. Slope is the steepness of a line, and it is measured by its slope. The slope of the straight line is the ratio of the rise to the run between both points.
The equation for slope is m = rise/run (rise over run), where m is slope.
The picture above shows an example of slope. To find the slope of a line, you find two points on the line, and imagine a triangle. Then, depending on how you think, you would move 2 times to the right, since the formula is m = rise/run. After that, you do the same thing, but move upwards 4 times instead of moving right, since we are trying to find the slope.
Rise = 4 Run = 2
m = rise/run
m = 4/2
m = 2/1
The run is horizontal (x-axis), and the rise is vertical (y-axis).
If the line is moving upwards/increasing, the slope is positive.
If the line is moving downwards/decreasing, the slope is negative.
TIP: In some cases, the line is a straight line with no rise or no run.
If the rise is 0 and the run is a #, the slope is always 0. EXAMPLE: 0/#
If the rise is a # and the run is 0, the slope is undefined. EXAMPLE: #/0
Therefore, horizontal lines have a slope of 0 (no rise), and vertical lines have a slope that is undefined (no run, cannot divide by zero).Another thing we learned was slope as a rate of change. A rate of change compares the change in one quantity relative to a change in another quantity.
Unlike slope, though, a rate of change is expressed in units! For example, km/h.
Basically, slope and rate of change are the same thing.

EXAMPLES: Loujain runs 25 km in 5 hours. What is her speed?
= 25/5
=5km/h
Sarah has a race with Sohyun. Sarah ran 30km in 3 hours, and Sohyun ran 36km in 6 hours. Who ran more?
Sarah- =30/3
=10 km/h
Sohyun- = 36/6
= 6 km/h
Sarah ran more.
Direct variation is the relationship between 2 variables in which one variable is a constant multiple of the other. Some characteristics of direct variation is how the graph will always be linear (straight line), the graph will always intercept the y-axis at the origin, and the equation for direct variation is always y = mx.
EXAMPLE: y=2x
D=5t
C=25h
H=10t
Partial variation is when the relationship between two variables have both a fixed and variable amount. Some characteristics of partial variation is how the fixed variable does not change- although the variable value changes, the graph intersects below or above the y-axis, the equation is always y = mx + b, and the line on a partial variation graph never passes through the origin.
EXAMPLE: C = 2.00 + 0.50n
T = 232 + 3n
y = 3.5x + 3
y = 0.2x + 5
TIP: the m (slope) and b (fixed cost) are constants.
m represents the constant of variation (multiple).
b represents the fixed, initial value.
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