(12C Platinum) Cubic Equation

02042019, 04:10 PM
(This post was last modified: 09022019 08:52 PM by Albert Chan.)
Post: #3




RE: (12C Platinum) Cubic Equation
Another way to get good guess is "look" at shape of curve
Example 1: x^3  4x^2 + 6x  24 = 0 x((x2)² + 2) = 24 ~ 2.88³ Any guess > 2 work. Say, guess = 3 X = 3 > 4.6667 > 4.1220 > 4.0051 > 4.0000 Example 2: 2x^3 + 3x^2 + 4x  5 = 0 x^3  1.5x^2  2x + 2.5 = 0 x((x0.75)²  2.5625) = 2.5 ~ 1.36³ If RHS is 0, we have roots 0.8508, 0, 2.3508, with LHS interval signs =  +  + Any guess < 0.8508 work. Say, guess = 1.5 X = 1.5 > 1.3649 > 1.3509 > 1.3508 Since LHS interval (0, 2.3508) also is negative, eqn might have 3 real roots. Indeed it does, 3 roots = 1.3508, 1.0000, 1.8508 

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Messages In This Thread 
(12C Platinum) Cubic Equation  Gamo  01122019, 09:27 AM
RE: (12C Platinum) Cubic Equation  Albert Chan  01122019, 01:39 PM
RE: (12C Platinum) Cubic Equation  Albert Chan  02042019 04:10 PM
RE: (12C Platinum) Cubic Equation  Thomas Klemm  02042019, 08:13 PM
RE: (12C Platinum) Cubic Equation  Albert Chan  02052019, 10:24 PM
RE: (12C Platinum) Cubic Equation  Gamo  02052019, 04:24 AM
RE: (12C Platinum) Cubic Equation  Thomas Klemm  02052019, 06:09 AM
RE: (12C Platinum) Cubic Equation  Thomas Klemm  02052019, 06:20 AM

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