Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

hi guys ... how are you ?!

if you know that : || L || = 4 ... || 2 L + M || = 13 ... the angle between the two vectors is θ = 120 ... what is the inner product of these two vectors ?! it looks easy but i dont know why they told me that my answer is wrong which was - 10 or 42

help please ...

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

inner product = dot product i think in which case

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

no man i meant with the two vectors L and M ... we have L but we have to get M first

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

oooh, you mean the product of L and M, not L and 2L+M

well then from that same equation i had

*Last edited by luca-deltodesco (2006-12-14 04:54:28)*

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

theta is the angle between L and M so we cant use it to get the first equation you said

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

ah... lol

*Last edited by luca-deltodesco (2006-12-14 07:09:03)*

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

guys ?!

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**Stanley_Marsh****Member**- Registered: 2006-12-13
- Posts: 345

I think you can draw a graph about it , 2L+M connect the two point of a parallelogram consists by M and 2L , knowing the length of 2L , and 2L+M ,and the angle , use geometry to solve it

Numbers are the essence of the Universe

Offline

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

the final answer is - 30 ... anybody ?

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

ok so we have

//quadratic in |M|

//+ is taken over -, since - would give a negative length to M, which is not allowed

*Last edited by luca-deltodesco (2006-12-15 20:05:45)*

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

**RauLiTo****Member**- From: Bahrain
- Registered: 2006-01-11
- Posts: 142

thaaaaanks btw its not 106 its 105

thans again

ImPo$$!BLe = NoTH!nG

Go DowN DeeP iNTo aNyTHinG U WiLL FinD MaTHeMaTiCs ...

Offline

**luca-deltodesco****Member**- Registered: 2006-05-05
- Posts: 1,470

RauLiTo wrote:

thaaaaanks btw its not 106 its 105

thans again

i corrected in my working out

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

Pages: **1**