# Math Help - Space diagonal

1. ## Space diagonal

In order to calculate the space diagonal on this cuboid:

I would do: $\sqrt{dab^2+c^2}$ right? Thanks.

2. ## Re: Space diagonal

Originally Posted by Paze
In order to calculate the space diagonal on this cuboid:

I would do: $\sqrt{dab^2+c^2}$ right? Thanks.
If you mean $\sqrt{d_{ab}^2 + c^2}$, then yes.

Edit: Since $d_{ab} = \sqrt{a^2+b^2}$, we have $d_{ab}^2 = a^2+b^2$, so an equivalent formula is:

$\sqrt{a^2+b^2+c^2}$