Find X Coord of Point A in Dot Product Homework

[ptnguyen]

Homework Statement

How would I find the X coordinate of point A.
So far I have:
A: ( X=? Y=-231.125" Z=175")
B: (X=0" Y=0" Z=144")

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Homework Equations

A^2+B^2=C^2

The Attempt at a Solution

https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/90/90135-0e378a7885d41efadbb78730140f9a77.jpg
Im thinking of 31^2+(-231.125^2)= hypotenuse= diagonal from B to A. Then I could solve for x since I have 2 sides of the triangle. But I'm not sure if it correct.

 

[drvrm]

Im thinking of 31^2+(-231.125^2)= hypotenuse= diagonal from B to A. Then I could solve for x since I have 2 sides of the triangle. But I'm not sure if it correct.

what is the angle between the vectors A and B ?
say the angle is Theta then one can use scalar product of these two tp proceed towards finding x or not ?