On a circular iron plate with a radius of 20cm, cut a rectangle with the largest area and the length twice the width, and calculate the area and perimeter of the rectangle

On a circular iron plate with a radius of 20cm, cut a rectangle with the largest area and the length twice the width, and calculate the area and perimeter of the rectangle

Let length and width be 2x and X respectively
Connect diagonals, which are diameters
therefore
（2X）^2+X^2=(20*2)^2
So x = 8 * (radical 5)
So the width is 8 * (root 5) cm
The length is 16 * (root 5) cm
The area of this rectangle (16 * radical 5) * (8 * radical 5) = 640 square centimeters
The perimeter of this rectangle is [(16 * radical 5) + (8 * radical 5)] * 2 = 48 * radical 5cm

The perimeter of a rectangle is 20cm long plus 4 width minus 1 area, and the area of the rectangle remains unchanged?

Length a, width b
a+b=10
ab=(a+4)(b-1)
Let's find out for ourselves

Use a 60cm long iron wire to form a rectangle. The ratio of length to width is 3:2. What is the area of the rectangle in cm2?

Length: 60 △ 2 × 33 + 2 = 30 × 35 = 18 (CM) width: 60 △ 2 × 23 + 2 = 30 × 25 = 12 (CM) 18 × 12 = 216 (square cm); answer: the area of this rectangle is 216 square cm