SaiBook.us Geometry

Lesson Example Discussion Quiz: Class Homework

Example

Title: Surface area for Cone & Cuboid

Grade: 6-a Lesson: S3-L1

Explanation: The best way to understand geometry is by looking at some examples. Take turns and read each example for easy understanding.

Examples:

A cone has a radius of 5 cm and a surface area of 100π square centimeters. Find the slant height of the cone.

Step 1a

The radius provided is 5 cm, and the surface area (A) is 100π square centimeters.
The formula for the surface area (A) of a cone is given by:
A = \$πr^2 + πrl\$

$1a$

Explanation: Given: radius = 5 cm, surface area (A) = 100π sq.cm.
Formula for surface area (A) of a cone: A = \$πr^2 + πrl\$.

Step 1b

We need to find the slant height (l).
Substitute the values :
100π = \$π5^2 + π5l\$
100π = 25π + 5πl
Subtract 25π on both sides of the equation:
75π = 5πl

Explanation: This step finds the slant height \$100π = π5^2 + π5l\$. We then solve for l by subtracting 25π from both sides of the equation.

Step 1c

Divide 5π on both sides of the equation: l = 15.
Therefore, the cone’s slant height(l) is 15 cm.

Explanation: Divide both sides of the equation by 5π. Therefore, the slant height (l) of the cone is 15 cm.