How to find a scalar product of two vectors?

H

hutch

New member
Joined
Dec 19, 2019
Messages
4
Can someone explain this question? It seems easy but i've spent way too long on it.

∙ = dot product
calculate the scalar product of
u(9,1) ∙ u (6,0)

where the base u = (u1 u2) has the following criteria:
u1∙u1=18
,u1∙u2=−9,
u2∙u2=9.

The answer is 918
 
what you've written doesn't make sense.

What does [MATH]\underline{u}(9,1)[/MATH] stand for?

[MATH](9\underline{u},~\underline{u} )[/MATH] ?
 
Romsek said:
what you've written doesn't make sense.

What does [MATH]\underline{u}(9,1)[/MATH] stand for?

[MATH](9\underline{u},~\underline{u} )[/MATH] ?
Click to expand...
yes thats right, they are the vectors
 
u = (u1, u2)
So I can only assume by u(9,1) you mean that u = (9,1)? Now if this is the case then how can u = (6,0) as well? Do you mean that v = (6,0)?

If u1∙u1=18, then u1 = +/-3sqrt(2)
If u2∙u2=9, then u2 = +/- 3
But then u1∙u2=−9 is not possible.

Post back with a clearly stated problem.
 
Hi, the problem is from an online quiz and i cant get the exact same problem. I've attached a similar problem with the same format.

The translation is "beräkna skalar produkten" = calculate the scalar product

"där basen u..." = where the base u meets the following criteria: ( u1 *u1 = 13 ect)

Note i've already passed this quiz, i just got stuck on this question and would really like to know how to solve it.
Thanks for your help.
 

Attachments

  • Picture1.png
    Picture1.png
    49.6 KB · Views: 5
Jomo said:
u = (u1, u2)
So I can only assume by u(9,1) you mean that u = (9,1)? Now if this is the case then how can u = (6,0) as well? Do you mean that v = (6,0)?

If u1∙u1=18, then u1 = +/-3sqrt(2)
If u2∙u2=9, then u2 = +/- 3
But then u1∙u2=−9 is not possible.

Post back with a clearly stated problem.
Click to expand...
see my post
 
hutch said:
calculate the scalar product of
u(9,1) ∙ u (6,0)

where the base u = (u1 u2) has the following criteria:
u1∙u1=18
,u1∙u2=−9,
u2∙u2=9.

The answer is 918
Click to expand...
It appears that you are saying that vectors are expressed in terms of a basis {u1, u2} where u1∙u1=18, u1∙u2=−9, and u2∙u2=9. So you want the dot product (9u1+1u2)∙(6u1+0u2).

To do that, just distribute and use the given facts. You will get 918 as the result.

It will be helpful if you can show an image of the problem, so we can confirm the notation they are using.
 
You must log in or register to reply here.
Top