Download Writing Equations of Lines Study Guide Given Information What to

Writing Equations of Lines Study Guide
Given Information
What to do: (Steps)
Graph
1. Find the y-intercept (b)
2. Count the rise over run,
or slope (m)
3. Plug them into slopeintercept form:
y=mx +b
Example
b=3
1 𝑤𝑒𝑛𝑡 𝑢𝑝 𝑜𝑛𝑒
m= (
)
2
𝑤𝑒𝑛𝑡 𝑟𝑖𝑔ℎ𝑡 2
y = mx +b
1
y= x +3
2
Slope and yintercept
1. Plug the slope (m) into
slope-intercept form
2. Plug the y-coordinate
(b) of the y-intercept
into slope-intercept
form: y=mx+ b
Slope is -3,
Point is (0, -2)
b = -2
m = -3
y = mx +b
y = -3x -2
Slope of Zero and
a point on line
(Horizontal Line)
* All points on a horizontal line
have the same y-coordinate.
Write the equation of line with slope of
0, passing through point (-2, 4).
* Equations are written
y = y-coordinate
y=4
Slope of Undefined
and a point on line
* All points on a vertical line have
the same x-coordinate.
Write the equation of line with slope of
undefined, passing through point (-3, 2).
* Equations are written
x= x-coordinate
x=3
(Vertical Line)
Slope and point on 1. Plug the slope (m) into
a line
the equation y=mx+ b
2. Use the given pt (x, y)
to substitute the x- & ycoordinates into the
equation y=mx+ b
3. Solve equation for b
4. Write equation
Write the equation of line with
slope of 1, passing through
point (-2, 3)
m=1
y= m x + b
3 = 1*-2 + b
3 = -2 + b
+2 +2
5=b
Equation: y = 1x + 5
Two points on a
line
y  y1
m 2
x2  x1
1. Use the 2 points to
calculate the slope of
line
2. Choose 1 of the given
points & the calculated
slope to substitute into
y= m x + b
3. Solve for b
4. Write equation
Write equation for line passing
through (-4, 4) and (2,-5)
−𝟓−𝟒
m= 𝟐− −𝟒 =
−𝟗
𝟔
=
−𝟑
𝟐
−𝟑
-5 = 𝟐 (2) + b
-5 = -3 + b
+3 +3
-2 = b
Equation: y =
−𝟑
𝟐
x–2
Parallel Lines
(equation) and
point
 Have the SAME
slope
m1  m2
Perpendicular
Lines
(equation) and
point
• slopes that are
the negative
reciprocal of
one another
1
m1  
m2
1. Substitute the slope from
Ex: through (1,7) and parallel to
original line (3 in this case)
y = 3x +5
into the equation of the
1) y = 3x +b
line
2) 7 = 3(1) +b
2. Substitute the given point
3)
(1,7) into the x and y values
3. Solve for b
4. Write equation
(substitute the value in
for b)
1. Id the slope of the
given line
2. Use negative (opposite)
reciprocal of given
slope as m
3. Use given point &
substitute coordinates
into y=mx+b for x & y
4. Solve for b
5. Write equation
4) y = 3x + 4
Ex: through (2,1) and perpendicular
to
y = -3x - 2
1) 𝑚1 = -3
2) 𝑚2 =
3&4) y=mx+b
1=
2
1
3
2
-3 -3
1
1
3
Y= x+
3
=b
1
3
(2) + 𝑏
1
3