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A-3 Straight Line Passing Through Two Points
Find the equation for the straight line passing through the two points (–2, 1) and
(–1, –4).
This problem is easy for students.
The straight line is found by substituting two points (–2, 1) and (–1, –4) into y = ax + b,
creating a system of simultaneous linear equations with two unknowns (a, and b).
Here we will use a regression line to obtain the result.
From the Main Menu, enter STAT Mode.
Input the following.
List 1 List 2
–2 1
–1 –4
Press1(GRPH) and then select 1(GPH1) .
This displays the two points on the screen. The straight line that passes between these two
points is the one we are trying to obtain.
Next, press 2(X) .
This calculates a = –5, b = –9 for y = ax + b.
Pressing 3(COPY) w substitutes y = –5x – 9 for GRAPH. Pressing 4(DRAW) draws
the straight line.
A-4 Parabola Passing Through Three Points
Find the equation of the parabola that passes through the following three
points: (–2, 1), (–1, –4), (1, 1).
This problem is difficult for students.
Here we will use the regression function to obtain the result.
From the Main Menu, enter the STAT Mode.
Input the following.
List 1 List 2
–2 1
–1 –4
11
Press1(GRPH) and then select 1(GPH1) .
This displays the three points on the screen. The parabola that passes through these three
points is the one we are trying to obtain.
Next, press 3(X^2) .
This calculates a = 2.5, b = 2.5, c = –4 for y = ax
2
+ bx+ c.
Pressing 3(COPY) w substitutes y = 2.5x
2
+ 2.5x–4 for GRAPH.
Pressing 4(DRAW) draws the parabola.
Mathematics with the Graphic Calculator
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