A 30 cm long, 20 cm wide rectangular cardboard four corners to a side length of 5 cm cube, and then fold along the dotted line into a cuboid What's the volume in cubic centimeters?

30-5×2=20(cm)
20-5×2=10(cm)
20×10×5=1000(cm³)
Therefore, the volume is 1000 cm and 179 cm;
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There is an 18 cm wide rectangular iron plate. After cutting out the square with a side length of 4 cm at the four corners, it is welded into an open iron box. The volume of the known iron box is 760 cubic meters
Cm. What's the area of the iron plate?

760 ﹣ 4 ﹣ 18-4x2 = 190 ﹣ 10 = 19cm
Length 19 + 4x2 = 27cm
Area 27x18 = 486 square centimeter
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It is known that the area of a sector is 100 square centimeter. Now we expand its center angle to 2 cm, and reduce its radius to 1 / 2 of the original. What is the sector area?

The central angle of the circle is doubled and the area is doubled, which is 100 × 2 = 200 (square centimeter)
If its radius is reduced by 1 / 2, its area will be reduced to 1 / 2 × 1 / 2 = 1 / 4
So the current area is: 200 × 1 / 4 = 50 (square centimeter)
The comprehensive formula is: 100 × 2 × (1 / 2 × 1 / 2) = 50 (square centimeter)
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The area of a sector is 100cm2, the central angle of its circle is 2 times larger, the radius is 0.5 times smaller, and the area is?

Let the center angle of the circle be n and the radius be r,
Sector area = n π R ^ 2 / 360,
The center angle of the circle is enlarged by 2 times, and the radius is reduced by half,
Sector area = 2n π (R / 2) ^ 2 / 360 = n π R ^ 2 / 720,
So the area is 50 cm ^ 2

The radius of the sector remains unchanged, and the central angle of the circle is reduced to half of the original area. How about the area?

The area is also reduced to half of the original

The central angle of the sector is expanded to twice of the original, and the radius is reduced to 12 of the original. At this time, the area of the sector is twice of the original area______ ．

If the original sector area is n π r2360, and the changed sector area is 2n π r24360 = n π R22 × 360, then the changed sector area is 12 times of the original area

The radius of a sector is expanded to three times of the original one, and the central angle of the sector is reduced to half of the original one. In this way, the area of the new sector is larger than that of the original one

The sector area formula is s = n π R ^ 2 △ 360 (where n is the center angle of the circle)
If the original radius is r, then it will be 3R after the change. If the original center angle is n, then it will be 1 / 2n after the change. Substituting the above equation, we can calculate that the ratio of the new sector area to the original sector area is 9:2
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The radius of a sector is expanded to three times of the original one, and the central angle of the sector is reduced to half of the original one. In this way, the area of the new sector is larger than that of the original one

Let the original radius be r and the center angle be a
The original sector area is
πR²xa/360
The new sector area is
π（3R）² x （a÷2）/360
=πR² xa/80
πR² xa/80：πR²xa/360=9：2

If the radius of a sector is reduced by 2 times and the central angle of the circle is increased by 2 times, the area of the sector will be reduced______
Such as the title

If the radius of the sector is r, the central angle of the sector is a
Then: the sector area is: S1 = pi * R ^ 2 * A / 360
If the radius is reduced by 2 times, the center angle of the circle is increased by 2 times
Then the sector area is: S2 = pi * (R / (2 + 1)) ^ 2 * ((2 + 1) * a) / 360 = pi * R ^ 2 * A / 3 / 360 = S1 / 3
If the radius of a sector is reduced by 2 times and the central angle is increased by 2 times, the area of the sector is also reduced by 2 times

It is known that the area of a sector is 100cm square. Now we expand its center angle by two times and reduce its radius by half. What is the sector area?

A 30 cm long, 20 cm wide rectangular cardboard four corners to a side length of 5 cm cube, and then fold along the dotted line into a cuboid What's the volume in cubic centimeters?