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**

**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 21,307

V # 1

Show that the vetcors a = (2,3,1), b = (5,-2,-4), and c = (10,-13,19) are mutually perpendicular.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Offline

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

a dot b = cosine of angle between them, cosine of 90 degrees is 0, so if a dot b is 0, they are perpendicular

a dot b = 2*5 + 3*-2 + 1*-4 = 10-6-4 = 0, a,b are perpendicular

a dot c = 2*10 + 3*-13 + 1*19 = 20 - 39 + 19 = 0, a,c are perpendicular

b dot c = 5*10 + -2*-13 + -4*19 = 50 + 26 - 76 = 0, b,c, are perpendicular

*Last edited by luca-deltodesco (2006-05-14 19:30:45)*

The Beginning Of All Things To End.

The End Of All Things To Come.

Offline

**ganesh****Moderator**- Registered: 2005-06-28
- Posts: 21,307

Very well done, luca-deltodesco!

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Offline

**angel_12****Member**- Registered: 2007-06-07
- Posts: 4

answer is already given...

waise that was a bit easy one!

Nothing is impossible..even impossible says I'm possible!

Offline

**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

i'd like to demand lots of vector proof problems, please!

can't find enough of them.

A logarithm is just a misspelled algorithm.

Offline

**anonimnystefy****Real Member**- From: Harlan's World
- Registered: 2011-05-23
- Posts: 16,016

hi ganesh

only one problem??? o.O

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

The knowledge of some things as a function of age is a delta function.

Offline

Pages: **1**