Each element in the result is the negative of the original, as seen below.
The negation of a matrix is formed by negating each element of the matrix:
-A = -1A
So, for example:
It will not surprise you that:
A + (-A) = 0
(Notice that that last zero is a bold-faced zero, designating the zero matrix.)
Look at the above fact. Can you think of a way to define matrix subtraction?