Luttrell 2012
87
Name: ______________________
Date: _____
6c –Writing Linear Equations
A needed skill is being able to write a model to represent values on a graph. A
model
is an
equation that represents the data. It may be an appro
x
imation, especially when the values do not
form a true shape of a line, parabola, etc. There are four equations to represent a line, and each
are useful when depending on a set of questions or given data. These equations are: slope-
intercept (y = m
x
+ b), point-slope (y - y
1
= m(
x
-
x
1
)), standard form (A
x
+ By = C, where A, B,
and C are integers), and double-intercept form (
x
/a + y/b = 1).
To write the equation of a line, you need either two points or a point and the slope. Let’s follow
two methods below with the points (1,-1) and (3,5). First find slope:
5
1
3
1
6
2
3
− −
−
= =
(
)
.
Method 1:
Method 2:
y
= m
x
+ b
y
-
y
1
=
m
(
x
-
x
1
)
y
= 3
x
+ b
y
- 5 = 3(
x
- 3)
5 = 3(3) + b
y
- 5 = 3
x
- 9
5 = 9 + b
y
= 3
x
- 4
- 4 = b
y
= 3
x
- 4
1. Write the equation that has slope
2. Write the equation that has m = 3
of ⅔ and y-intercept of -7.
and passes through (0,-2).
3. Write the equation that passes
4. Write the equation that passes
through (0,2) and (3,1).
through (0,3) and (2,1).
5. Write the equation that passes
6. Write the equation that passes
through (2,1) and (4,-3).
through (1,2) and (10,2).
7. Write the equation that passes through (-6, 3) and (3,7).
