Why is the formula for the area of the side of a cone this The formula given in the book is s = π (R '& sup2; + R & sup2; + r'l + RL) I can understand that π R '& sup2; + π R & sup2; is the area of the top and bottom Why is π (r'l + RL)

Why is the formula for the area of the side of a cone this The formula given in the book is s = π (R '& sup2; + R & sup2; + r'l + RL) I can understand that π R '& sup2; + π R & sup2; is the area of the top and bottom Why is π (r'l + RL)

The fan ring and trapezoid share the same area formula: (upper bottom + lower bottom) * height / 2, where the upper and lower bottom are respectively the circumference 2 π R, 2 π R ', and the height is the generatrix L, so the area formula π (r'l + RL) is obtained
To be specific: compared with triangle and sector area formula, both are consistent (bottom * height / 2), trapezoid is the difference between two triangles, and fan ring is also the difference between two sectors, so it can be deduced that fan ring and trapezoid area formula are consistent

All formulas of side area

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Area of cylinder side = perimeter of bottom * height
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How to do the sixth grade mathematics volume II page 6 of Beijing Normal University Edition

Give it a try. 4x3.14 = 12.56 decimeters 12.56x5 = 62.8 square decimeters [4 divided by 2] square x3.14 plus 62.8 = 75.36 square decimeters
Lian Yi 100.48 244.9 is not 25.12