# Homework Help: Length of diagonal from bottom to top

1. Jul 29, 2017

### zak100

1. The problem statement, all variables and given/known data

I have to find the length of a diagonal from bottom to top. I dont know which formula i would be using? Please see the attachment for more information.
2. Relevant equations

May be pythagorous theorem. But i dont know which sides i have to select
3. The attempt at a solution
Sorry i need some hint.
Zulfi.

2. Jul 29, 2017

### Nidum

Add one more line to the sketch and the way to solve this problem should become easier for you to see . The added line goes from point A to the point vertically below point B .

Last edited: Jul 29, 2017
3. Jul 29, 2017

### SammyS

Staff Emeritus
To add to @Nidum 's comment:

The added line goes from point A to the corner of the box vertically below point B .

4. Jul 29, 2017

### Staff: Mentor

You'll need to use Pythagoras theorem twice.

5. Aug 1, 2017

### Kaura

Try thinking of the line drawn as the vector <10, 7, 2>

6. Aug 2, 2017

### zak100

Hi,
Thanks everybody. Post# 3 provided a clue but i came to know about this when i solved the problem. The other clue is the application of pythagorus theorem on rectangular solids which i got from the following link: https://www.google.com.pk/imgres?im...ved=0ahUKEwiA__Hz3LjVAhVHBcAKHQACAMEQ9QEIJzAA

Let K be the point below B & C is connected to both A & K
AK^2 = AC^2 + CK^2
AB^2 = AK^2 + BK^2
AB^2 = AC^2 + CK^2 + BK^2 = 100 + 49 + 4 therefore AB = 3sqrt(17).

Thanks.

Zulfi.