why does sin(90) differ from sin(π/2) when I punch this in the calculator? Am I punching in the wrong buttons when I do the sin(90)?
sin(90) = .8939
whereas sin(π/2) = 1
They are both quadrantal (90), right?

Are you switching from radians to degrees first? Use the MODE key and see if that helps. (Or do sin(90*π/180).)

That article talks about Degrees, DMS, and Radians notations. While the MODE button lets you choose between having either Radians or Degrees implied in all calculations, the ANGLE menu gives you the °/r postfix operators for forcing a behavior on a per-quantity basis.
@bb010g, yeah, when I switched the mode, that did the trick. to me, I think it's counterintuitive. When the calculator "defaults" to radians, I would expect the trig functions to come up as using pi symbols versus, the decimals.
You can get symbols like π in your answers by using a CAS (either by an engine or calculators like the Nspires with CAS, TI-89s, or HP Prime). You can always divide by π if you want.
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