Surface Area of a Pyramid | MathHelp.com - By MathHelp.com
Transcript
| 00:0-1 | a regular pentagonal pyramid has a base edge of seven | |
| 00:05 | centimetres and the lateral area of 210 square centimeters . | |
| 00:11 | Find the slant height of the pyramid . Remember that | |
| 00:15 | ? The formula for the lateral area of a pyramid | |
| 00:19 | is 1/2 perimeter of the base times the slant height | |
| 00:26 | were given that the lateral area is 210 square centimeters | |
| 00:32 | , but we don't know the perimeter of the base | |
| 00:36 | . However , we do know that the pyramid has | |
| 00:39 | a base edge of seven . And since the base | |
| 00:43 | is a regular pentagon , we know that it has | |
| 00:47 | five congruent sides . So the formula for the perimeter | |
| 00:52 | of the base is five times the length of a | |
| 00:56 | side or five times 7 , Which is 35 . | |
| 01:07 | Yeah . Now , since the lateral area is 210 | |
| 01:13 | And the perimeter of the base is 35 . We | |
| 01:17 | can plug this information into the formula To get 210 | |
| 01:23 | equals 1/2 times 35 times out . Simplifying on the | |
| 01:32 | right side , We have 210 Equals 35 L . | |
| 01:39 | Over two . Now , to get rid of the | |
| 01:43 | fraction , we multiply both sides of the equation by | |
| 01:48 | two . Uh huh . Yes . To get 420 | |
| 01:58 | Equals 35 L . And dividing both sides by 35 | |
| 02:06 | . Yeah . Okay . Yeah . We find that | |
| 02:10 | 12 equals l . So the slant height of the | |
| 02:16 | given pyramid is 12 cm . |
Summarizer
DESCRIPTION:
This lesson covers the definition of perpendicular lines. Students learn the definition of perpendicular lines and use algebra to find the measures of angles in problems that involve perpendicular lines. Students are also asked to determine whether given information is sufficient to determine if two lines are perpendicular.
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