The TI-89 calculator distinguishes, using different keys, between the unary operation of negation and the binary operation of subtraction.
|To enter a negative number, use the negation key, , the grey key located to the left of the key. To subtract two numbers, use the black minus key located above the addition key.|
For example, to subtract -5 from 17, compute 17 - (-5). Press
To enter the function y1 = -x, use the negation key, not the minus sign.