why isn't 1+2sin(7pi/6) = 0

Question

TI inspire CX ii 1+2sin(7pi/6) show equal to -2E-13 not 0 why?

 

This gives 0 answer on an TI-83 series but not on an nspire.

Answer 1

I don't own a TI inspire CX II, but I'm going to guess the difference lies in "rounding error".  On my TI-84 Plus, when I enter "sin(7PI/6)" it returns "-.5".  If it returns anything else, you probably are seeing a "rounding error" somewhere in the sin() function.  For all practical purposes, any computer that gives a floating point answer with an exponent of less than -7 can be considered to be zero.