
Find the Lateral area and surface area of the regular pyramid.

Answer to Problem 3CYU
L = 207.8m2
S = 332.5m2
Explanation of Solution
Given:
Formula Used: The Lateral area L of a regular Pyramid is
L=12Pl , where l is the slant height and P is the perimeter of the base .
The Surface area S of a regular Pyramid is
S=12Pl+B , where l is the slant height, P is the perimeter of the base and B is the area of the base .
Calculation:
The base of the pyramid is regular hexagon.As shown in the figure, find the base of the right
Using Pythagoras Theorem :
So, the length of the base b = √102−82=√100−64=6m
Now, the base is a regular hexagon .Divide the base in 6 equal
Draw the right angled triangle out and find the base:
Now, first find the value of x = 360°12=30°
Also,
tanx=a6....................[tanθ=length of side opposite to θlength of side adjacent to θ]⇒tan30°=a6⇒a=6tan30°...........[multiply each side by 6]⇒a=6⋅1√3.............[tan30°=1√3]⇒a=6√3
Now, the length of base of each triangle =
2⋅6√3=12√3⋅√3√3=4√3m
Hence , each side of the hexagon is 4√3m
Perimeter of the base = P = (length of each side )(number of sides ) = 6⋅4√3=24√3m
So, the Lateral area = L=12Pl=12(24√3)(10)=207.8m2
The area of one section of the hexagon , which is a triangle with base 4√3m and height
6 m is 12(base)(height)=12(4√3)(6)=12√3cm2
So, the area of the base = B = 6×12√3=124.71cm2 ....[there are 6 equal triangles ]
So, the surface area of the pyramid :
S=12Pl+B=207.8+124.71=332.5m2
Hence ,
L = 207.8m2
S = 332.5m2
Chapter 12 Solutions
Geometry, Student Edition
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