Homework Help: Geometry plz help

Posted by Ryan on Sunday, November 29, 2009 at 7:56pm.

A rectangular solid has a top face with surface area of 28 ft, a front face with surface area of 20 ft, and a side face with surface area of 70 ft. What is the volume of this solid?

Geometry plz help - MathMate, Sunday, November 29, 2009 at 9:46pm
There are two ways to approach the problem:
1. Calculate the side lengths, a,b and c.
ab=28....(1)
ac=20....(2)
bc=70....(3)

Therefore by dividing ac by bc, we get
a/b=2/7
substitute a=2b/7 into equation (1) gives 2b/7*b=28 => b²=98 => 7√2

You can calculate similarly the other sides.

2.
You are looking for the product abc, from which ab=28
So
abc=ab*bc*√((a/b)/ab)
All the products are known, the quotient has been calculated in part 1.
So the volume abc can be calculated directly.
Geometry plz help - Ryan, Monday, November 30, 2009 at 7:31pm
umm still lost.....
Geometry plz help - MathMate, Monday, November 30, 2009 at 11:15pm
Did you try method 1 or method 2?

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