Hi this is Rob. I am going to show you how
to make a Quadratic Formula Program in the
TI 84 Plus CE Graphing Calculator. This is
also going to be an introduction to programming
the TI 84 Plus CE.
Remember a quadratic equation is in the form
ax squared + bx + c. To solve for x on a quadratic
equation we usually factor the equation. However,
sometimes the quadratic is too difficult to
factor, so we use the quadratic formula which
is x equals negative b plus or minus the square
root of b squared minus 4ac all over 2a.
Here is how to enter a program into the TI
84 Plus CE to calculate the quadratic formula
when you know a, b and c of the quadratic
equation.
We will be using the programming language
of TI Basic to create this program.
To make a new program, press the program button
here. Use the right arrow key to move over
to NEW and press enter.
This screen pops up and we want to create
a new program so press enter or the 1 key
to begin creating a new program.
This window pops up. We need to create a name
for our program. I am going to name our program
QUADFORM for quadratic formula. You see the
cursor is flashing an letter A. This means
that we are in Alpha Mode. The calculator
automatically put us in the green button Alpha
mode. We need to be in this mode to input
capital letters which are in green above the
keys in our key pad.
The maximum name length for programs are 8
characters. Press the enter key.
Now we are ready to start adding lines of
code to our QUADFORM program.
To go to the list of commands that are available
for our program, from here we press the program
button.
At the top you see four headings, Control
Commands, Input Output Commands, Color Commands,
and Executables. The Executables are programs
within programs. Right now you only see one
program listed, QUADFORM. That is the program
that we are currently working on. There are
many more commands available for TI Basic.
To see the complete list of commands press
the blue 2nd key then the catalog button,
which is the zero key at the bottom of the
key pad.
For our program we need to start with a prompt,
so go to the I/O heading. And select number
2:Prompt by pressing the 2 on the keypad or
use the down arrow key to highlight it and
press enter.
We want the program to prompt us to enter
the three variables of A, B, and C. Go into
alpha mode by pressing the green alpha key
here. Now enter A comma, green alpha button,
B, comma, green alpha button, C. That is the
first command line. The program is saved as
we type, so don’t worry if you have to stop
in the middle of programming, it is automatically
saved. When you are finished with the first
command line, press the enter key.
Now we are ready to enter our next command
line. Remember our quadratic formula. Because
there is no plus or minus command we must
do two separate commands. The first command
we will do is the plus.
Enter an open parenthesis here, negative b,
make sure you use the negative sign here,
apha key, B, plus, squared root, which is
the 2nd key and this x squared key, enter
an open parenthesis here, B squared, which
is the alpha key, B, then this x squared button.
Minus 4, A, C, closed parenthesis.
Which is closing the inner parenthesis, now
we need to closed the outer parenthesis with
another closed parenthesis. Then divide, open
parenthesis, 2, A, closed parenthesis. Now
we want to store that calculation into a variable
we will call D by pressing this store key
here, and then alpha key, D. We are finished
with this command line, press the enter key
for the next command line.
The next command is the same as above except
that the plus sign is a minus sign, and then
we store this calculation into the variable
E.
Press the enter key for the next command line.
Now we want to tell the program to display
our answers to the quadratic formula.
Press the program button, go to I/O, and choose
number 3:Disp for display. Now enter our variables
D comma E.
Now we are completely finished with this program.
Remember that the program is saved as we typed
it.
To run the program we quit the editor by pressing
the blue 2nd button and the mode button.
Now before we run this program we need to
set the calculator to display complex numbers.
Remember a complex number is a real number
and an imaginary number combined. Many times
when we can not factor a quadratic equation
easily, it is because it has complex roots
in the solution.
To change the calculator’s mode to display
complex numbers press the mode key here, this
window pops up. Go down using the down arrow
key to REAL and to the right of REAL is a+bi.
This is the complex number notation.
Use the right arrow key and highlight it.
Now press the enter key. OK, it is set to
display complex numbers. Now go to the home
screen by pressing the blue 2nd key and then
the mode key. If you do not change the calculator’s
mode to display complex numbers and you run
this program with a quadratic equation with
complex roots, you will get this error message.
In REAL MODE, all calculations must result
in a real number.
Now let’s run our program. Press the program
key. Select the program from the Exec Menu.
Right now it is the only program we have so
press the enter key.
Now our program QUADFORM is loaded up. We
want to calculate the x values for the following
quadratic equation, x squared plus 3x minus
4 equals zero. The standard form is Ax + Bx
+ C, so our A=1, B= 3, and C equals negative
4.
We are ready to run the program by pressing
the enter key. The A=? is the prompt command
at work, in response we enter the value for
A which in this case is 1. enter a 1 and press
the enter key. Now the program is asking for
the B value, which is 3, enter a 3 and press
the enter key. Now enter the C value which
is a negative 4 and press the enter key.
And there to the bottom right is the answer,
x equals negative 4 and x equals one.
Now if you have another equation to solve
press the enter key and the program runs again,
asking for a new A value. To exit the program
just press the blue 2nd key and mode key and
now press the clear button.
The only other problem with this program is
if the roots of the quadratic equation is
a square root, it will not display the square
root, the program will calculate the square
root for the answer.
OK that is it. That is how to program the
quadratic equation into your TI 84 Plus CE
graphing calculator. If you like this video
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