Vector identity show that question

[fleeceman10]

Homework Statement

u and v are vectors

Homework Equations

show that : mod(u x v)^2 +(u.v)^2 = mod(u)^2 x mod(v)^2

The Attempt at a Solution

I thought about let u =(a,b,c) let v = (x,y,z) and then doing the calculations. However I have done this but then squaring everything out at the end will take ages and I'm certain that's not how they want it done.

 

[Dick]

Homework Statement

u and v are vectors

Homework Equations

show that : mod(u x v)^2 +(u.v)^2 = mod(u)^2 x mod(v)^2

The Attempt at a Solution

I thought about let u =(a,b,c) let v = (x,y,z) and then doing the calculations. However I have done this but then squaring everything out at the end will take ages and I'm certain that's not how they want it done.

The cross product and the dot product are related to a sin and a cos of the angle between u and v.

 

[fleeceman10]

thats very helpful (sarcasm). To make it clear, I want a solution

 

[Mark44]

thats very helpful (sarcasm). To make it clear, I want a solution

Per the rules of this forum, we don't provide solutions.
Here's an excerpt from the rules (https://www.physicsforums.com/showthread.php?t=414380):
On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

Also, please don't post the same problem in multiple sections.

 

[fleeceman10]

Per the rules of this forum, we don't provide solutions.
Here's an excerpt from the rules (https://www.physicsforums.com/showthread.php?t=414380):
On helping with questions: Any and all assistance given to homework assignments or textbook style exercises should be given only after the questioner has shown some effort in solving the problem. If no attempt is made then the questioner should be asked to provide one before any assistance is given. Under no circumstances should complete solutions be provided to a questioner, whether or not an attempt has been made.

Also, please don't post the same problem in multiple sections.

look if people want to post solutions let them. Stop being such a spoil sport.

 

[Mark44]

It's not about being a spoil sport - these are the rules. Moderators can and do enforce the rules by deleting any posts that provide complete solutions. It is NOT the purpose of this site to do your work for you.

 

[fleeceman10]

It's not about being a spoil sport - these are the rules. Moderators can and do enforce the rules by deleting any posts that provide complete solutions. It is NOT the purpose of this site to do your work for you.

well maybe I will find a different forum. One where petty rules do not hamper the education of it's members. Know of any?

 

[Evo]

That's an excellent idea.

 

[HallsofIvy]

well maybe I will find a different forum. One where petty rules do not hamper the education of it's members. Know of any?

You think that "education" means being told the answers? Essentially, you are saying that you believe you are not capable of thinking. I am very sorry to hear that and hope it is not true. If it is true, then this forum cannot help you. I doubt that you will be able to find a forum that simply hands you the answers and, even if you can, that will not help you pass tests.