USing TI-Nspire CAS to solve a trig inequality

[jb]

Is there a way to get the CAS calculator to solve the inequality
5cosx>0? WHne I do it like entering in "non" trig inequalities, we
get nice answers. On this one, I even enter in the "such that" symbol
"|" and enter a domain like 0<t<2pi and it gives a value of n1 or n2
in the answers.....any suggestions?

[Joe]

@n followed by a number is TI's unusual way of describing constants
that are normally indicated by using the letter c, or C, or k. For
example (4.@n1-1).pi\2 means (4k-1)pi/2

[jb]

I have seen them before, but if I specify a range of values, that is
not supposed to happen.....it does not happen with equations...just
inequalities.....

> > in the answers.....any suggestions?- Hide quoted text -
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> - Show quoted text -

[Joe]

The | symbol is the "with" symbol and when there is more than one
constraint on the right side, the constraints must be separated with
the word and. Entering your problem this way: 5cos(x)>0|x>0 and
x<2pi where the pi symbol is used, the problem returns the original
expression 5cos(x)>0 which for any cas is just an indication that it
cannot solve the problem. You might contact TI about incorporating
that capabililty but I doubt that they will.

> > - Show quoted text -- Hide quoted text -

[jb]

Thanks for everyone's suggestions......you do not have to use "and" on
the nspire CAS with other inequalities.....it does seem as though TI
needs to fix this!

[Wayne]

No need for the "and" in this problem either. Entered as
solve(5*cos(x)>0,x) "with" 0<x<2*pi, the solution from my Nspire
returns two inequalities, both of which must be satisfied. With the
@n variable = 0, the two (simultaneous) inequalilties resolve to the
solutions 0<x<pi/2 and with the @n variable = 1, the two inequalilties
resolve to the solutions 3*pi/2<x<2*pi . These are the correct
intervals for the solution for 5*cos(x)>0 on 0<x<2*pi .
Wayne

[jb]

My question is why does it have to have the "n" in there in the first
place??

[Eric Findlay]

Check out the discussion entitled "What does it mean? n followed by a
number, e.g. 'n23'". It's discussed at great length there. Basically,
it's a unique identifier for a variable in the solution.

--
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--
Eric Findlay
AKA Eagle-Man

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