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How to fit a curve to data on a TI-83 Plus

By E-Code · updated

With X in L1 and Y in L2, press STAT, ▶ to CALC, 5 for QuadReg and ENTER. It gives a, b and c of the best parabola y = ax² + bx + c; ExpReg (item 0) fits growth and decay the same way.

Before you start

Type the data into the lists first: STAT, ENTER, X values in L1 (0, 1, 2, 3, 4) and Y values in L2 (5, 20.1, 25.4, 20.9, 6.6), then 2nd QUIT.

STAT ENTER 0 ENTER 1 ENTER 2 ENTER 3 ENTER 4 ENTER ▶ 5 ENTER 2 0 . 1 ENTER 2 5 . 4 ENTER 2 0 . 9 ENTER 6 . 6 ENTER 2nd MODE

Step by step

  1. Open STAT. STAT Press STAT. A thrown ball's times (0 to 4 s) are already in L1 and its heights in metres in L2.
  2. The CALC tab. ▶ Press ▶ to CALC. Item 5 is QuadReg, the best parabola y = ax² + bx + c.
  3. Pick QuadReg. 5 Press 5. QuadReg is pasted on the home screen.
  4. Calculate. ENTER Press ENTER. With no lists after it, QuadReg uses L1 for X and L2 for Y.
  5. Read the fit. y = −4.9x² + 20x + 5. a = −4.9 is half of gravity's −9.8 m/s², b = 20 m/s the throw speed, c = 5 m the start height. ExpReg (item 0) fits growth and decay.

What the screen shows

y = −4.9x² + 20x + 5. a = −4.9 is half of gravity's −9.8 m/s², b = 20 m/s the throw speed, c = 5 m the start height. ExpReg (item 0) fits growth and decay.

Look for c=5 on the screen.

Try it with the keys lit up

This guide is one of E-Code's Learn lessons. Open it on E-Code's TI-84 calculator and each key lights up in turn as you press it.

Try “Fit a curve to data” on the TI-84 calculator

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Physics programs for the TI-84 Plus CE:

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