<image>As shown in the figure, Figure 1 is a rectangle with a length of 2m and a width of 2n (m>n), cut along the dotted line in the figure into four congruent small rectangles, and then arranged according to Figure 2 to form a larger square.
(1) Please use two methods to express the area of the shaded part in the figure (only expression is required, no simplification necessary).
(2) Compare the two results from (1), what kind of equality can you observe?
(3) Use the equality derived from (2) to solve the following problem: if mn=12 and m+n=8, find the value of m-n.
