1, the side length of a square is a, and the area is a2 (representing the square of a, the same below). The side length is expanded by 3 times, and its area is expanded by 8 times; If the side length is reduced to 1, its area will be reduced to1;

2, b, pay attention to the diameter;

If you want the area of a circle, you must calculate the area of the inner circle and the outer circle, and then subtract it to get the area of the circle. First, calculate the area of the inner circle as ∏r2, that is, the square of 3. 14×7 = 153.86 cm2, and then calculate the area of the outer circle as: 3. 14×(2+7

4. Similar to the third question, calculate the radius first. The radius of the outer circle is ÷∈ 2 = 25.12 ÷ 3.14 ÷ 2 = 4, and the radius of the inner circle is ÷∏.

5. First calculate the area of the triangle, that is, the area of the circle: ∏r2=7850, that is, the area of the triangle is 7850, and then calculate the height of the triangle = area ÷ base ÷ 2 = 7850 ÷157× 2 =100;

6. The square of π× (5/3r)