What's the lateral area of the frustum of a cone?

The formula for calculating the side area of the frustum is: S=πrl+πr'l (where r and r' are the radii of the two bottom surfaces and l is the length of the bus).

For example, the upper and lower radius of the frustum is 1, and the second height is 1. Find the side area of the frustum of a cone

Solution: After the frustum side is unfolded, it is actually a circular section.

It is also trapezoidal deformation, and the trapezoidal formula can be used.

The formula of trapezoidal area is: (upper bottom+lower bottom) * height /2.

Upper sole: upper aperture circumference =2* 1*3. 14, and lower sole: lower aperture circumference =2*2*3. 14.

Height: namely, the side length of frustum = 1.4 14, namely √2.

∴ frustum side area: (2 *1* 3.14+2 * 3.14) *1.414/2 =13.32.