Question 30468
This problem is due just to the order in which you apply the operators ^ and -.

It's true that a negative number times a negative number yields a positive number, so (-6)*(-6) = 36.

However, when you say -6^2, you could either mean "find the square of -6" or "find the square of 6 and then multiply it by -1". Clearly, these two interpretationes yield different results: the first one is 36; the 2nd one is -36.

Your graphing calculator processes first the square and the minus, so the result is -36 (the 2nd interpretation). In your scientific calculator, you're telling it to take -6 and multiply it by -6. The result of this is clearly 36.

This problem is solved by correctly applying parenthesis. If you want to say "-6 squared" you should write (-6)^2. However, if you want to find the square of 6 and multiply it by -1, then you could write -(6^2) in order to avoid confusion.