下图由 2 个正方形 ABCD 和 DEFG 组成。X 是 GD 上的一个点,Y 是 DE 上的一个点。BC = 7 cm,FE = 6 cm,且 XD = DY = YE。

  1. (a)

    求阴影部分的总面积。

  2. (b)

    未阴影部分占整个图形的几分之几?

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完整解法

16(a)

1. Find the area of the shaded part in the left square ABCD.

The shaded region is triangle ABC, which is exactly half of the square ABCD.
Area of square ABCD =7×7=49 cm2= 7 \times 7 = 49\text{ cm}^2
Area of shaded triangle ABC =12×49=24.5 cm2= \frac{1}{2} \times 49 = 24.5\text{ cm}^2

2. Determine the lengths of the segments XD, DY, and YE in the right square DEFG.

The side length of square DEFG is 6 cm6\text{ cm}, so DE=6 cmDE = 6\text{ cm}.
Since YY is on DEDE and DY=YEDY = YE, we have:
DY=YE=6÷2=3 cmDY = YE = 6 \div 2 = 3\text{ cm}
We are also given XD=DYXD = DY, so XD=3 cmXD = 3\text{ cm}.
The length of GX=GD−XD=6−3=3 cmGX = GD - XD = 6 - 3 = 3\text{ cm}.

3. Calculate the area of the shaded triangle FXY by subtracting the unshaded triangles from the square DEFG.

Area of square DEFG =6×6=36 cm2= 6 \times 6 = 36\text{ cm}^2
The unshaded region in square DEFG consists of three right-angled triangles:

  1. Area of △FGX=12×FG×GX=12×6×3=9 cm2\triangle FGX = \frac{1}{2} \times FG \times GX = \frac{1}{2} \times 6 \times 3 = 9\text{ cm}^2
  2. Area of △XDY=12×XD×DY=12×3×3=4.5 cm2\triangle XDY = \frac{1}{2} \times XD \times DY = \frac{1}{2} \times 3 \times 3 = 4.5\text{ cm}^2
  3. Area of △YEF=12×YE×EF=12×3×6=9 cm2\triangle YEF = \frac{1}{2} \times YE \times EF = \frac{1}{2} \times 3 \times 6 = 9\text{ cm}^2

Area of shaded △FXY=36−(9+4.5+9)=36−22.5=13.5 cm2\triangle FXY = 36 - (9 + 4.5 + 9) = 36 - 22.5 = 13.5\text{ cm}^2

4. Find the total shaded area.

Total shaded area =Area of △ABC+Area of △FXY= \text{Area of } \triangle ABC + \text{Area of } \triangle FXY
Total shaded area =24.5+13.5=38 cm2= 24.5 + 13.5 = 38\text{ cm}^2

答案

38 cm238\text{ cm}^2

16(b)

1. Calculate the total area of the figure

Area of square ABCD =7×7=49 cm2= 7 \times 7 = 49 \text{ cm}^2
Area of square DEFG =6×6=36 cm2= 6 \times 6 = 36 \text{ cm}^2
Total area =49+36=85 cm2= 49 + 36 = 85 \text{ cm}^2

2. Calculate the total shaded area

Shaded area in ABCD (Triangle ABC) =12×7×7=24.5 cm2= \frac{1}{2} \times 7 \times 7 = 24.5 \text{ cm}^2
For square DEFG, DY+YE=6 cmDY + YE = 6 \text{ cm}, so DY=YE=3 cmDY = YE = 3 \text{ cm}. Thus XD=3 cmXD = 3 \text{ cm}.
Area of unshaded triangles in DEFG:
Area of △FGX=12×6×3=9 cm2\triangle FGX = \frac{1}{2} \times 6 \times 3 = 9 \text{ cm}^2
Area of △XDY=12×3×3=4.5 cm2\triangle XDY = \frac{1}{2} \times 3 \times 3 = 4.5 \text{ cm}^2
Area of △FEY=12×6×3=9 cm2\triangle FEY = \frac{1}{2} \times 6 \times 3 = 9 \text{ cm}^2
Shaded area in DEFG (Triangle FXY) =36−9−4.5−9=13.5 cm2= 36 - 9 - 4.5 - 9 = 13.5 \text{ cm}^2
Total shaded area =24.5+13.5=38 cm2= 24.5 + 13.5 = 38 \text{ cm}^2

3. Calculate the unshaded area and the required fraction

Unshaded area =Total area−Total shaded area=85−38=47 cm2= \text{Total area} - \text{Total shaded area} = 85 - 38 = 47 \text{ cm}^2
Fraction of figure unshaded =4785= \frac{47}{85}

答案

4785\frac{47}{85}

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