Using a graphing calculator to check simplification problems

USING A GRAPHING CALCULATOR TO CHECK

SIMPLIFICATION PROBLEMS

You can always check your answer to a simplification problem using your calculator (or you can use another method that will be shown here). This example is taken from the January 2010 Math B Regents (number 13)

22 yxxy

This example is taken from the January 2010 Math B Regents (number 13)Which of the following is equivalent to

A B C D

yx 1

yx 1

yx 1

yx 1

Without a calculatorChoose a value for x and y. Let’s say x = 2 and y = 1Now check the value you get when you substitute these values of x and y in the original expression and see what value you get

22 yxxy

22 1221

141

31

31

Now check each answer for x = 2 and y = 1 and see if you get -1/3

A

B

C

D

yx 1 1

11

121

111

121

yx

1

yx 1

31

121

yx 1

31

31

121

This is the only one that has the same value as our original expression

Using the graphing calculator to do this

You can store values for variables into your calculator. First we’ll store x = 2

Press the following sequence: 2, STO, XYour screen should show this Press enter:

Now our calculator has x set equal to 2

We will do the same for y: we will store 1 into yThe sequence we will press is: 1, STO, APLHA, 1

Your screen should show this:

Press enter:

Now check the value of the original expression using our values

22 yxxy

The sequence of keys we will press:Left parenthesis, ALPHA, 1, - (minus not negative), X, Right parenthesis, division symbol, left parenthesis, X, x^2 button, - (minus not negative), ALPHA, 1, x^2 button, ENTER

After entering this sequence of buttons, this is what you should see on your screen:

The next half:Here’s what you should have on your screen

Pressing enter you should get:

If you want to convert your decimal to a fraction, press the following sequence:

MATH, 1 Here’s what you’ll see on your screen

Press ENTER

Check the other expressions in a similar manner. The only answer that matches will be D.

Be carefulYou must be careful about the values you choose for x and y

For example in our last example22 yxxy

We could not let x = y since that would cause division by 0 which is illegal.

You should only use this as a checking tool, NOT as your primary method of simplifying.