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Re: Different answers in mathematica and my calculator.

• To: mathgroup at smc.vnet.net
• Subject: [mg125593] Re: Different answers in mathematica and my calculator.
• From: Peter Pein <petsie at dordos.net>
• Date: Tue, 20 Mar 2012 02:22:38 -0500 (EST)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <jk70c1$12t$1@smc.vnet.net>

Am 19.03.2012 11:04, schrieb Nile:
> 4/(3Power[2(-2)+3, (3)^-1])
>
> I get -(4/3) (-1)^(2/3) in Mathematica but only -4/3 on my calculator.
>
powers with non-integer exponents are not unique in the domain of 
complex numbers. Try Root[]:

4/(3 Root[#^3 - (2 (-2) + 3) &, 1])
>
> N[Sec[8/(8 Sqrt[2])]]/Degree to get Cos^-1 of 8/(8 Sqrt[2]) and it gives me 75 deg instead of 45...
>
> I'm not sure what I'm doing wrong, I tried in Wolfram Alpha and it gives me the same thing.

I am afraid, you mixed the inverse function cos^(-1)(x) with the 
reciprocal (cos(x))^(-1). Use ArcCos and FunctionExpand (the latter to 
convert Degree to Pi/180):

ArcCos[8/(8 Sqrt[2])]/Degree // FunctionExpand

>
> Thank you.
>
> -Francis
>