<image> Figure 1 is a rectangle with a length of 2m and a width of 2n. It is evenly divided into four small rectangles along the dashed lines in the figure, and then rearranged to form a square as shown in Figure 2.
(1) What do you think is the side length of the shaded square in Figure 2? _______ 
(2) Find the area of the shaded part in Figure 2 by two different methods. Method 1: ____________ Method 2: ______.
(3) By observing Figure 2, can you write down the equal relationship between the following three algebraic expressions: (m+n)^{2}, (m-n)^{2}, mn? ______________________________ .
(4) Based on the equivalence relationship in question (3), solve the following problem: If a-b=7 and ab=5, then (a+b)^{2}= _____.
(5) If a+b = -3 and ab = -28, then a−b=________________ _.