Homework Help: Big question on vectors!

1. Dec 3, 2007

I need help with adding vectors. I basically want to know when do I use the pythagorean method and when do I simply add them.

This has me confused.

2. Dec 3, 2007

3. Dec 3, 2007

salman213

(1,1,1) + (1,1,1) = (2,2,2)

magnitude of the vector is equal to

square root of 2^2 + 2^2 + 2^2 = root pf 12

4. Dec 3, 2007

what?

I mean if its 8m N + 6 M E [example]

should I do the theorem or no?

5. Dec 3, 2007

cristo

Staff Emeritus
Draw a diagram. You will see that those vectors form two sides of a right angled triangle, of which the hypotenuse is the resultant.

6. Dec 3, 2007

so if they are on a different axis: phythagorean thereom?

7. Dec 3, 2007

salman213

if they are collinear then add them otherwise if the vectors are perpendicular (ie - 1 is North and the other is East) then you use the pythagorean thereom to find the resultant

8. Dec 3, 2007

cristo

Staff Emeritus
To get the magnitudes then, yes, if two vectors point in the same direction you can add them to get the resultant. If not, it is always safer to draw a diagram.

Note that, however, if you want to simply add vectors, you can do it component-wise; so if a=(x,y), b=(u,v), then a+b=(x+u,y+v).

9. Dec 3, 2007

rock.freak667

If the angle between them is 0 or 180, you add or subtract as necessary...if the angle is 90 degrees...the hypotenuse is the resultant

if the angle is any other obtuse angle...you use the parallelogram law