Casio wins lawsuit against Chinese calculator copy

[Albert Chan]

(06-27-2021 06:34 PM)celltx Wrote:  In the end of the video, it shows that the fake calculator returns completely incorrect answer.

To be fair to the fake calculator, equation setup (Newton's method) have 2 solutions.

f(x) = (21+x)/x - 8
f'(x) = -21/x^2

nt(x) = x - f(x)/f'(x) = x - ((21+x)/x - 8) / (-21/x^2) = x - x*(x-3)/3
nt(x) = x       → x = 0 or 3

We should setup equation by scaling away denominator

f(x) = (21+x) - 8x
f'(x) = -7

nt(x) = x - f(x)/f'(x) = x - (21-7x)/(-7) = 3       → x = 3

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Tips: it is safer to put equation on the stack (without "=" key), before SOLVE
This way, we can recover equation with ↑ key

0 STO X                // guess in X, such that equation does not ERROR
21+X-8X =           // equation now on stack
SOLVE SOLVE       → X = 3