Dr. Byrne
Fall 2010
Math 112
Slope-intercept equation of a line: y  mx  b
m = slope of the line
b = where the line intercepts the y-axis
Worksheet 1.3: Finding the Slope Given 2 Points
Given two points: P= x1 , y1  , Q= x2 , y2  ,
rise y 2  y1
the slope between them =
=
.
run x 2  x1
Find the equation of the line containing the given points, by finding the slope and then solving for
the y-intercept.
1. P = (1,1), Q = (2,4)
2. P = (-2,1), Q = (2,-4).
3. P = (2, 3 ), Q = (-3, 3 ).
2
2
sketch:
sketch:
sketch:
calculate slope:
calculate slope:
calculate slope:
solve for the y-intercept:
solve for the y-intercept:
solve for the y-intercept:
equation for the line:
equation for the line:
equation for the line:
Find the slope and y-intercept of the line, and sketch its graph.
11.  3x  4 y  2
9. y  1 x  3
4
slope:
y-intercept:
slope:
y-intercept:
sketch:
sketch:
x
x
y
Application: Total Cost. The Cellular Connection charges $60 for a phone
and $29 per month under its economy plan. Write an equation that can be
used to determine the total cost, C(t), of operating a Cellular Connection
phone for t months. Then find the total cost for 6 months.
Application: Temperature and Depth of the Earth. The surface temperature of
the Earth is approximately 68 F. Every kilometer deeper into the Earth, the
temperature increases by 18 degrees. Write an equation that describes the
temperature of the Earth T(d) as a function of the depth d inside the Earth.
What is the temperature of the Earth 3 kilometers down?
Month
t
y
Cost
C(t)