/sci/ - Science & Math

[Anonymous No.3714284]

I have a question regarding my ti-30x II science calculator:
Why does (-8)^(2/3) give me a domain error?

Isn't the answer supposed to be 4?

[Anonymous No.3714291]

First, it square roots the number... then it'll raise it to the 3rd power. Since you can't square root a negative, it won't go past that.
It'll be able to to the power of 1/3, though.
It's just a shitty way of calculating it that it does.

[Anonymous No.3714295]

Probably cause you can't take the root of a negative.

[Anonymous No.3714299]

<span class="math">-2+2\;i\;\sqrt{3}[/spoiler]

[Anonymous No.3714307]

The calculator doesn't work with exact numbers, so it doesn't know the exponent is exactly 2/3. Consider (-8)^(2000001/3000000). That's not a real number.

[Anonymous No.3714316]

>>3714295
>>3714291
So I suppose the other way to do this problem, then, would be like this: 3*radical(-8)^2 = 4

[Anonymous No.3714318]

>>3714284
First calculator does 2/3. It's not equal 2/3 in mathematical sence, but rather 0.666...667 - a finite fraction due to rounding. That way the next function (^) does not know that power is exactly 2/3, all it knows is 0.66...67. Power function is probably implemented as x^y=exp(ln(x)*y) for non-integer y. And since I assume it's not high-end calculator, it doesn't do complex numbers, therefore ln(-8) is undefined.

[Anonymous No.3714322]

>>3714316
Just add the negative in manually I guess

[Anonymous No.3714336]

I thought TIs had rationals. I swore mine did.

[Anonymous No.3714341]

>>3714318
>>3714307
>>3714322
>>3714299

Thanks for the insights and recommendations everyone.