# Question: 3-D Diagonal

## Comment on 3-D Diagonal

### Hi,

Hi,

I just wanted to confirm, when you meant that the hypotenuse should be corresponding to the Pythagoras triplets, you did not mean even the legs of the right triangle should be corresponding right?

When working with right triangles, we should always be on the lookout for Pythagorean triplets. This means examining the legs AND the hypotenuse for Pythagorean triplets or MULTIPLES of Pythagorean triplets.

### Hey just wanted to know that

Hey just wanted to know that at 1:37, how did you conclude that the computed diagnol of 10 inches is perpendicular to the height(7 inches) of the cuboid?

### Great question.

Great question.

At 1:37 in the video, the diagonal in question is the hypotenuse of a right triangle with legs that are 6 inches and 8 inches long (see 1:21 in the video for more on this)

So, if we let h represent the hypotenuse of this right triangle, we can write: 6² + 8² = h², and when we solve that equation, we see that h = 10

Since that 10-inch diagonal lies on the bottom of the "box" then the side with length 7 must be perpendicular to that 10-inch diagonal.

Does that help?

### Hey Brent,

Hey Brent,
In one of the previous questions, you had used a different approach. The answer then will be √245.
Check this out- https://gmatclub.com/forum/each-edge-of-the-above-cube-has-length-1-if-an-ant-268193.html

### There's a big difference

There's a big difference between the video question above and the linked question: https://gmatclub.com/forum/each-edge-of-the-above-cube-has-length-1-if-a...

In the linked question, the ant walks from point A to point B along the OUTSIDE of the cube. In the video question above, we're looking for the DIRECT distance from A to B.

Does that help?

Cheers,
Brent

### Hi Brent, can you please

Hi Brent, can you please explain this question. I was unable to understand what the question means. I was trying to solve it by applying formula sqrt(side^2 + side^2 + sides^2).
https://gmatclub.com/forum/the-surface-distance-between-2-points-on-the-surface-of-a-cube-is-the-305873.html