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length of diagnoal of a cube

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by Anurag@Gurome » Thu Sep 01, 2011 8:28 pm
venmic wrote:Is length of diagnoal of a cube

Length = √(a²+b²+c²)
Since all the sides in a cube are of same length, say a, so the Diagonal length = √(3a²) = a√3
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by Abhishek009 » Fri Sep 02, 2011 6:47 am
venmic wrote:Is length of diagnoal of a cube

Length = √(a²+b²+c²)
this is actually the formula of a cuboid....

however you can derive the formula very easily , coz all sides of a cube are equal so ,


a = b = c

hence √(a²+b²+c²) => √(a²+a²+a²)= √ 3 a²

Or we can say

Diagonal of a cube is a √ 3 ....
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by Brent@GMATPrepNow » Fri Sep 02, 2011 7:20 am
venmic wrote:Is length of diagnoal of a cube

Length = √(a²+b²+c²)
Yes, it's the length of a cube's diagonal (for a cube, a=b=c).
It's also formula for the length of the diagonal of a box.

So, for example, if a box has dimensions 2x3x7, then the length of the diagonal (from one point to the point furthest away) will equal root(2^2 + 3^2 + 7^2), which equals root(62)

I have a free video (video #12) at https://www.gmatprepnow.com/module/gmat-geometry that explains this formula.

Cheers,
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