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The four corners form two squares with a side length of 2cm and an area of 2 * 2 * 2 = 8 square cm;
If the side length of a square is a (a is greater than 4), then the shadow area = (A-8) square centimeter

It is known that the side length of the square ABCD is 13. The distance from a point outside the plane ABCD to each vertex of the square is 13cm. M.N

）Proof: pass n as NN / / / DC to BC to n/
Pass m as mm / / / AB, pass PB to m / and connect M / n/
M / N / / / AB and PM: Ma = 5:8
Mm /: ab = 5:13 and ab = 13 mm / = 5
Similarly, NN / = 5 can be obtained
Mm / / / AB AB AB / / CD / / NN/
MM///NN/ MM/=NN/
The quadrilateral mm / N / N is a parallelogram
MN//M/N/
M / N / face PBC
Mn face PBC Mn / / face PBC

As shown in the figure, ABCD is a square with side length A. draw semicircles with AB, BC, CD and DA as diameters respectively, and calculate the area of shadow part surrounded by these four semicircle arcs

π（A
2）2×1
2×4-A2
= Pi
2A2-A2
=（π
2-1）A2；
So the answer is: (π
2-1）A2

The side length of the square ABCD is 20 cm AB.BC.CD . Da draw a semicircle for the diameter and find out the area of the shadow formed by four semicircle arcs

Analysis and as shown in the figure, there are four semicircles in the square, and there are four overlapping parts of petal shape, Add up the area of four semicircles (i.e. two circles) and subtract the square area to get the shadow area. The area of a semicircle: (20 ￣ 2)? × 3.14 ￣ 2 = 157 (square centimeter) the area of four semicircles: 157 × 4 = 628 (square centimeter) or directly calculate the area of two circles: (20 ￣ 2)? × 3.14 × 2 = 628 (square centimeter). The area of square: 20 × 20 = 400 (square centimeter) 628-400 = 228 (square centimeter) a: the shadow area is 228 square centimeters

As shown in the figure ABCD is a square with side length A. draw semicircles with AB, BC, CD and DA as the diameters, and calculate the area of the shadow part surrounded by these four semicircle arcs

There are four identical shadow parts. First find one block, first find its half, s = 1 / 4 * pi * (A / 2) - 1 / 2 * (A / 2) square
The total area is 8s

As shown in the figure, ABCD is a square with side length A. draw semicircles with AB, BC, CD and DA as diameters respectively, and calculate the area of shadow part surrounded by these four semicircle arcs

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To the second floor error correction, is a quarter circle!
The shadow area should be 25 π - 50

As shown in the figure, in the square ABCD, BD is 20 cm, and C is on the circumference with a as the center, so the area of the shadow is______ .

The area of square = 20 × (20 △ 2) = 200 (square centimeter);
Area of sector = 1
4×3.14×202，
=3.14×100，
=314 (square centimeter);
Area of shadow part = 314-200,
=114 (square centimeter);
A: the shadow area is 114 square centimeters
So the answer is: 114 square centimeter

In the parallelogram ABCD, AE = EF = FB. Ag = 2CG, the area of triangle GEF is 6 square centimeters, and what is the area of parallelogram?

Let the height of △ ABC with BC as the bottom edge is h, and the height of △ EFG with FG as the bottom edge is h;
Because AC: Ag = AB: AF = 3:2
So FG ‖ BC
So △ ABC ∽ AFG
So FG: BC = 2:3, that is BC = 3
2FG
Because AE = EF = FB
So h: H = 1
3, i.e. H = 3 h
Because the area of the triangle EFG = FG × h △ 2 = 6 (square centimeter)
So the area of the triangle ABC = BC × h △ 2 = 3
2FGX3h÷2=9
2 × (FG × h △ 2) = 27 (square centimeter)
So the area of the parallelogram ABCD = the area of two triangles ABC = 54 (square centimeter);
A: the area of the parallelogram is 54 square centimeters

In the parallelogram ABCD, AE = EF = FB. Ag = 2CG, the area of triangle GEF is 6 square centimeters, and what is the area of parallelogram?

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