My Math Forum Factoring and calculator issues

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 April 1st, 2012, 05:51 PM #1 Newbie   Joined: Apr 2012 Posts: 3 Thanks: 0 Factoring and calculator issues hey everyone, i have a calc 2 test coming up on taylor polynomials and power series. when i type in the convergence points in the original equations, i sometimes have to input (-1)^"variable" for some reason, the calculator spits out an answer with sin and cosines that take up the entire screen. for example, (-1)^x*(-1)^x puts out 2COS(180X)^2-1+2SIN*(180X)...blablabla...i tried every combination of settings but it still gives me the same BS answer. i know this is simple algebra, but some equations are super long and i want to use the calc to do it for me. does anyone have any idea why this is happening? thanks!
 April 1st, 2012, 05:59 PM #2 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,963 Thanks: 1148 Math Focus: Elementary mathematics and beyond Re: Factoring and calculator issues What calculator are you using?
 April 1st, 2012, 06:51 PM #3 Global Moderator     Joined: Nov 2006 From: UTC -5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms Re: Factoring and calculator issues Presumably when you give it (-1)^x it gives you a series expansion for the expression in terms of x about 0: (-1)^x = exp(x log -1) = 1 + (x log -1) + (x log -1)^2/2 + ...; judging from the 180s, it's probably in degree mode rather than radian mode.
 April 2nd, 2012, 05:19 AM #4 Newbie   Joined: Apr 2012 Posts: 3 Thanks: 0 Re: Factoring and calculator issues i have a TI Nspire CX CAS. i tried changing to radians, but it just changed to 2cos(n*pi^2)-1+2sin(n*pi)...etc.. i know this is a very simple problem, i'm just trying to figure out why the calc is making such a big issue out of it hehe.
 April 2nd, 2012, 05:28 AM #5 Newbie   Joined: Apr 2012 Posts: 3 Thanks: 0 Re: Factoring and calculator issues and i never entered it as a series, just (-1)^x*(-1)^x thanks!
April 2nd, 2012, 08:45 AM   #6
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Re: Factoring and calculator issues

Quote:
 Originally Posted by robman and i never entered it as a series, just (-1)^x*(-1)^x
Right, but the only thing it knows to do with (-1)^x is to turn it into a series. (Don't trust me, though -- try it!)

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