Dawnbridge

TI-84 Plus CE field manual for IB Math

Everyone · 16 of 45

16

Finding roots of a polynomial

All courses

Use the calculator's polynomial root finder to enter the coefficients of a polynomial and read all real roots.

Goal

Find the real roots of ​x3−7x+6=0.

1

Open the polynomial root finder: press , choose PlySmlt2, press any key if the app's about screen appears, then choose 1: Polynomial Root Finder.

2

Set the order to 3, since the polynomial is cubic. Press (the soft key under NEXT) to move to the coefficient entry screen.

3

Enter the coefficients in descending powers of ​x: 1, 0, -7, 6. The ​x2​ coefficient is ​0, so it must be included. Use for the negative sign in -7.

NORMALFLOATAUTOREALRADIANMP
PLYSMLT2 APP
1x³+0x²+-7x+6=0
x₁=-3
x₂=1
x₃=2
MAINMODECOEFFSTOREF◀▶D
4

Press (the soft key under SOLVE). The TI-84 lists the roots of the polynomial.

Result

The roots are ​x=−3,  ​x=1, and ​x=2.

Your turn

Work each one on your calculator, then check the answer.

  1. 1

    Find all real roots of ​x3−13x+12=0.

  2. 2

    Find all real roots of ​x3−19x+30=0.

  3. 3

    Find all real roots of ​x3−21x−20=0.