Calculator Solution:
The Statistics features of the graphing calculator can be used to
write the equations of straight lines given points. 
1.
Enter the points into lists L1 and
L2.
(See
Basic Commands for
entering data.) Be careful to keep the x and corresponding
y coordinates lined up horizontally.


2.
Choose STAT. Arrow to the right
to CALC at the top of the screen.
Choose #4:LinReg(ax+b). 

3.
On the home screen you will need
to tell the calculator which lists contain your points. If you
also wish to quickly graph your new line, include
Y1. (L1 and L2 are above the numbers 1 and 2 on the calculator.) (To get Y1: Choose VARS → YVARS, #1Function. Choose Y1)

The Y1 is only needed if you wish
to also see the graph of the line. 
4.
Hitting ENTER will show the screen at
the right. "a" is the slope, and "b" is the yintercept.
If
you hit y = , you will see the equation
for the line. Hitting GRAPH will
show the graph.

