TI-83/84 Calculator Help in MATH 141 / 168

Finding an Exact Fractional Value of a Decimal
From your home screen, if you have calculated a value which is not an integer value, you can determine whether or not it is a rational number and can be written as an exact fraction by hitting MATH and choosing option 1: Frac and then hitting ENTER. The reduced fraction for your value should appear if it is a rational number.

Finding the Intersection Point of Two Lines
  1. Graph the two functions by entering the slope-intercept form of the lines into Y1 and Y2. These are located under the Y= button.
  2. Go to CALC which is found by pressing 2nd TRACE.
  3. Select option 5:intersect.
  4. The calculator will prompt you for the first and second curves you want to intersect. The cursor will blink on a function and show the function name in the upper left corner of the screen. When it blinks on Y1, press ENTER & when it blinks on Y2, press ENTER.
  5. The calculator will then ask you to guess where the intersection point is located. Use your right and left arrow keys to move to the intersection point and press ENTER.
  6. The intersection point will appear at the bottom of the screen.

Linear Regression
  1. Enter your x and y values into lists. To do this, hit STAT and select 1:Edit.... If you have anything in L1 or L2, cursor up to the name of the list, hit CLEAR and ENTER. Now just enter in your values one at a time by pressing ENTER after each number.
  2. To find the regression equation, first hit STAT, cursor right to CALC and select option 4:LinReg(ax+b). Now press 2nd 1 , 2nd 2 , to specify the x list and y list. (REMEMBER THE COMMAS! You do not have to specify the lists if you are using L1 and L2 for your x and y-values, respectively.) Hit VARS, cursor right to Y-VARS, select 1:Function... and Y1 (or whichever function you would like) to specify where the regession equation will be saved. You should now see the following on your home screen:

    LinReg(ax+b) L1, L2, Y1 or LinReg(ax+b) Y1 (if you are using L1 and L2 for your lists)

  3. Now, press ENTER. The following should appear on your screen:


    Your regression line is the equation now saved under Y1. If you don't have the r stuff, then you need to turn your diagnostics on. To do this, hit 2nd 0, and cursor down to select DiagnosticOn. When this comes up on your home screen, press ENTER and it should say Done.
  4. To graph the regression line with the data points, first make sure your stat plot is turned on. To do this, hit 2nd Y= and select 1.... by pressing ENTER. You can then highlight any of the options you would like. Now just hit GRAPH. If you don't see anything, adjust your window size under WINDOW and ZOOM.
  5. To find a y value from your regression line when given an x value, go to the main calculator screen and call up your function name (VARS, cursor right to Y-VARS, select 1:Function... and Y1 (or whichever function your line is in)) and then open the left parenthesis, type the x value and close your parenthesis. OR... hit CALC (2nd TRACE) and select option 1:value. Then just enter the value for x.
  6. To find an x value from your regression line when given a y value, enter the y value under Y2 and then find the intersection point between Y1 (your regression line) and Y2.

If you have a TI-83 Plus or any version of the TI-84, when you see directions to hit the MATRX button, you need to hit 2nd x^(-1).



Compound Interest and Effective Rates of Interest for Non-Continually Compounded Accounts
For both of these types of problems, go to FINANCE on your calculator. If you have the regular TI-83, this is found by hitting 2nd x^(-1). If you have the TI-83 Plus, this is found by hitting the blue APPS button and selecting option 1:Finance....