Casio FX-115MS bug
11-24-2018, 07:25 PM (This post was last modified: 10-30-2019 11:34 PM by Albert Chan.)
Post: #12
 Albert Chan Senior Member Posts: 1,984 Joined: Jul 2018
RE: Casio FX-115MS bug
Solving cubic with hyperbolic sine formula, discovered Casio FX-115MS asinh bug
(asinh bug also hit my Casio FX-3650P ...)

Solve X³ + 11 X - 1000100 = 0 for X, using formula X = -2 √(r) sinh(1/3 * asinh(s/r^1.5))

asinh(s/r^1.5)) = asinh(-500050/(11/3)^1.5) = asinh(-71220.70789) = -11.86817286 ???

Even my pocket Casio FX-260Solar get this right, asinh(-71220.70789) = -11.86668608

My guess the problem is the Quadratic Solver subtraction cancellation.

Solving sinh(x) = (exp(x) - 1/exp(x))/2 = -71220.70789, solver gives exp(x) = 7.01e-6
x = ln(7.01e-6) = -11.86817286 (same as the produced bug)

As a temporary fix, force asinh to use big root:

asinh(x) = ln(√(x²+1) + x) = - ln(√(x²+1) - x) = - asinh(-x)

asinh(x) = sign(x) * asinh(|x|)

asinh(-71220.70789) = -1 * asinh(+71220.70789) = -11.86668608
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 Messages In This Thread Casio FX-115MS bug - Albert Chan - 10-31-2018, 07:02 PM RE: Casio FX-115MS bug - klesl - 11-01-2018, 11:14 AM RE: Casio FX-115MS bug - ijabbott - 11-01-2018, 08:16 PM RE: Casio FX-115MS bug - G. Cook - 11-02-2018, 09:14 PM RE: Casio FX-115MS bug - Albert Chan - 11-03-2018, 02:41 PM RE: Casio FX-115MS bug - Albert Chan - 11-05-2018, 08:58 PM RE: Casio FX-115MS bug - Albert Chan - 11-07-2018, 08:15 PM RE: Casio FX-115MS bug - Albert Chan - 11-07-2018, 10:47 PM RE: Casio FX-115MS bug - Albert Chan - 11-08-2018, 04:17 PM RE: Casio FX-115MS bug - Albert Chan - 11-24-2018 07:25 PM RE: Casio FX-115MS bug - ijabbott - 11-24-2018, 08:28 PM RE: Casio FX-115MS bug - klesl - 11-07-2018, 08:33 PM RE: Casio FX-115MS bug - Albert Chan - 11-08-2018, 02:51 PM RE: Casio FX-115MS bug - brickviking - 11-28-2018, 01:01 AM

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