Answer to Question #149221 in Geometry for marshy taray

Question #149221
3. Find the volume and lateral surface area of the frustum of a regular square pyramid whose altitude is 38 cm and whose base edges are 10 cm and 20 cm respectively.
1
Expert's answer
2020-12-07T20:14:39-0500

We know that ,if a,ba,b and hh are the base edge,top edge and height of a frustum of a regular square pyramid,then formula for volume and lateral surface area are -

Volume(V)=(1/3)(a2+b2+ab)×h(V) =(1/3)(a^2+b^2+ab)×h

Lateral surface area(F)=2(a+b)(((ab)/2)2+h2)(F)=2(a+b)\sqrt(((a-b)/2)^2+h^2)

Now according to the given problem,

a=20cma=20 cm , b=10cmb=10cm ,h=38cmh=38cm

Therefore required volume of the frustum of square pyramid is

V=(1/3)×((20)2+(10)2+(20×10))×38V=(1/3)×((20)^2+(10)^2+(20×10))×38

=(1/3)×(400+100+200)×38=(1/3)×(400+100+200)×38 cm3cm^3

=(26600/3)=(26600/3) cm3cm^3

and Lateral surface area is

F=2×(20+10)×(((2010)/2)2+382)F=2×(20+10)×\sqrt(((20-10)/2)^2+38^2)

=2×30×(25+1444)=2×30×\sqrt(25+1444) cm2cm^2

=60×1469=60×\sqrt1469 cm2cm^2


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