Plus42 Equations, Preview Release

[Thomas Okken]

(11-30-2021 03:11 PM)Albert Chan Wrote:  Is this a feature, or a bug ?

[...]

Plus42:
eqn = "1 + (1-SIN(X))^3", go in "CALC", 0 "X" 3 "X", "X" (to solve)

375.E-3 - i831.E-3 // complex solution ?

It's a feature.

Since X appears only once in the equation, Plus42 uses the direct solver, which finds the solution algebraically, by transforming the equation to 1+(1-SIN(X))^3=0, then (1-SIN(X))^3=-1 (subtracting 1 on both sides), then 1-SIN(X)=500E-3+i866E-3 (raising to the power 1/3 on both sides), then SIN(X)=500E-3-i866E-3 (subtracting from 1 on both sides), then X=375E-3-i831E-3 (taking the arcsine on both sides).

If you set REALRES mode, there will be an error during this procedure when it tries to calculate (-1)^(1/3), and it will switch to the numerical solver and find an extremum.