? In rectangular ABCD, AB=CD and AC=BD.

? Therefore, the perimeter of the shaded part is the same as the perimeter of the filled rectangle, which is (3+7)×2=20 (decimeter).

(2) Below the left

? In rectangular ABCD, CD=AB, AC = BD = 5cm.

? Therefore, the perimeter of the shaded part is the perimeter of the supplementary rectangle plus the AC and BD lengths,

? That is, (13+17) × 2+5× 2 = 70 (cm).