In a 8 cm long, 5 cm wide rectangular cardboard cut a largest circle, circle area is______ Square decimeter

In a 8 cm long, 5 cm wide rectangular cardboard cut a largest circle, circle area is______ Square decimeter

2, = 3.14 × 6.25, = 19.625 (square centimeter), = 0.19625 square decimeter; answer: the area of a circle is 0.19625 square decimeter

Use a rectangle with a length of 31.4cm and a width of 5cm to form a cylinder. What are the areas of the two ground circles to be added?

Take 31.4 as the circumference of the bottom surface of the cylinder, and then calculate the radius of the cylinder, 31.4 △ 3.14 △ 2 = 5cm
Area of circle = 3.14 × 5 square = 78.5

The circumference of a rectangle is 10cm, and the length is 3cm longer than the width. The length of the rectangle is x (CM), and the width is y (CM). According to the meaning of the title, the binary linear equations about X and y can be listed

x-y=3
2(x+y)=10