Fit a parabola to data
Find the curve y = ax² + bx + c that best matches points that bend.
When data curves up or down, like the height of a thrown ball, a parabola fits better than a line. The calculator finds a, b and c in y = ax² + bx + c.
The example uses x = 0 to 4 and y = 3, 4, 9, 18, 31. These points lie exactly on y = 2x² - x + 3.
Classic Graphing 84
Start on the main screen: Press 2nd then mode (QUIT) to get back to the home screen. Pressing clear on a menu also backs out of it.
Type x into L1 and y into L2.
stat10enter1enter2enter3enter4enter▶3enter4enter9enter18enter31enterOpen STAT, move to CALC and choose QuadReg.
stat▶5Move down to Calculate and press enter.
▼▼▼▼enter
You should seeQuadReg a=2 b=⁻1 c=3
Classic Scientific 30
Start on the main screen: Press 2nd then mode (QUIT) to leave any menu or screen and return to the calculation screen.
Type x into L1 and y into L2.
data0enter1enter2enter3enter4enter▶▲▲▲▲▲3enter4enter9enter18enter31enterOpen the STAT menu (2nd then data) and choose QuadraticReg. Accept the lists with enter.
2ndstatdata4enterenterenter
You should seey=ax²+bx+c 1:a=2 2:b=-1 3:c=3
Natural Scientific 991
Start on the main screen: Press MENU, then 1 (Calculate) to return to the main calculation screen. AC clears the line you are on.
Open Statistics and choose y=a+bx+cx². Type the x column.
MENU630=1=2=3=4=Go back to the top of the table, one column right, and type the y column.
▶▲▲▲▲▲3=4=9=18=31=ACPress OPTN and choose Regression Calc.
OPTN3
You should seey=a+bx+cx² a=3 b=-1 c=2
This model names the constant term a and the x² coefficient c, the other way round from the graphing models.
Natural Color Graphing
Start on the main screen: Press MENU then 1 to open Run-Matrix, the main calculation screen. Press EXIT to back out of a bar or screen, and SHIFT then EXIT (QUIT) to return to the app start.
Type x into List 1 and y into List 2.
MENU20EXE1EXE2EXE3EXE4EXE▲▲▲▲▲▶3EXE4EXE9EXE18EXE31EXEChoose CALC (F2), then REG (F3), then X² (F3).
F2F3F3
You should seea=2 b=-1 c=3
Tips
- You need at least three points with different x values. More points give a more trustworthy curve.