Originally Posted by
FrameOfMind Remember BIDMAS (Brackets, Indices, Division, Multiplication, Addition, Subtraction).
The order of operands is very important, and this is where you're having trouble.
-9 is essentially like saying 0 - 9, you just omit the 0.
Now, from BIDMAS, we know that everything in brackets is evaluated first, and that indices/multiplication is evaluated before subtraction.
So (-9^2) is like saying (0 - 9^2). You evaluate the index first, then you subtract the result from 0.
0 - (9)(9) = 0 - 81 = -81
Whereas, in (-9)^2 you evaluate everything in brackets first, so (0 - 9)^2 = (-9)(-9) = 81, because multiplying an even number of negatives together results in a positive.
I hope that was clear enough.