Test analysis:

As can be seen from the figure, the shaded part in the "Smooth sailing" figure is the same as the two triangles "1" and "2" in the square, both of which are isosceles right triangles. According to the trapezoid in Figure B, it is equal to the right-angled side of Triangle 2, and the side length of small square is equal to the right-angled side of Triangle 2.

As can be seen in Figure A, the diagonal of the big square is equal to the side length of the right triangle with four shaded parts.

Given that the side length of a big square is 8 and the diagonal =,

So the side length of the shadow triangle =

The area is:.

Comments: The difficulty of this question is moderate, which mainly examines students' mastery of the knowledge points of isosceles right triangle and square in jigsaw puzzles. Grasping the graphic relationship between equilateral triangles in two graphs is the key to solving the problem.