Use three iron wires to form the figure below. The largest area is () A. Rectangle B, square C, circle D, cannot be determined

Use three iron wires to form the figure below. The largest area is () A. Rectangle B, square C, circle D, cannot be determined

c

A 20 cm long wire is used to form a plane figure, of which the () shape has the largest area
A: Triangle B: square C: rectangle D: circle
It's not about the answers,

For a triangle, if the area of a square is the largest, then the side length is 20 / 3. If the area of a square is 10 root sign 3 / 3 * 10 / 3 = 100 / 9 * root sign 3. If the side length of a square is a = 20 / 4 = 5, if the area of a rectangle is 25, then the width of a rectangle is a, B (A & gt; b), then a + B = 10, and area = AB = (10-B) B. obviously, the maximum value is only a = b = 5

Use a 125.6cm long wire to encircle the city, a square and a circle. Which figure has the largest area? How much?

It's round, of course
a=125.6/4=31.4(cm)
r=125.6/(3.14*2)=20(cm)
S positive = 31.4 * 31.4 = 985.96 (cm2)
S circle = 3.14 * 20 * 20 = 1256 (square centimeter)

Xiao Ming uses two pieces of 62.8 cm long iron wire to encircle the city into a square, rectangle and circle. Is the area of their encirclement the same? How about the formula

It's not the same
one
Square side length a, perimeter C = 4 * a, so a = C / 4 = 62.8 / 4 = 15.7 (CM)
Square area s = a * a = 246.49 (square centimeter)
two
A square is a special rectangle. If the length of the rectangle must be greater than the width, its area must be less than the square with equal perimeter. This can be determined by the sum of two numbers. The greater the difference between the two numbers, the smaller their product
three
Circumference C = 2 * pi * r, so r = C / (2 * PI) = 62.8 / (2 * 3.14) = 10 (CM)
Circle area s = pi * r * r = 3.14 * 10 * 10 = 314 (cm2)
To sum up, when the perimeter is equal, the enclosed area is different, circle > square > rectangle