## Vectors dot product and cross product help

1. The problem statement, all variables and given/known data
Vectors A and B (both with the lines over it) lie in an xy plane. Vector A has magnitude 8 and angle 130 degrees, Vector B has components Bx=-7.72 and By=-9.2.
a)What is 5(vector A) dot vector B?
b)What is 4(Vector A) cross 3(vector B) in unit vector notation and magnitude angle notation with spherical coordinates?

2. Relevant equations
Vector A dot Vector B=abcos(phi)
Other vector equations that can apply to this that I don't know maybe...

3. The attempt at a solution
I figured that I try to find the vector B by doing the Pythagorean theorem with the two components of B and I get -12 as magnitude. After that I'm not even sure what to do, like for the 5(vector A) do I multiply the angle and magnitude by 5 then do the Vector A dot Vector B=abcos(phi) equation? Same question applies to b and how do I turn the magnitude and the angle into unit vector notation and magnitude angle notation? Thanks in advance.

EDIT: Forget A, I solved it
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Recognitions:
Homework Help
 Quote by maximade 1. The problem statement, all variables and given/known data Vectors A and B (both with the lines over it) lie in an xy plane. Vector A has magnitude 8 and angle 130 degrees, Vector B has components Bx=-7.72 and By=-9.2. a)What is 5(vector A) dot vector B? b)What is 4(Vector A) cross 3(vector B) in unit vector notation and magnitude angle notation with spherical coordinates? 2. Relevant equations Vector A dot Vector B=abcos(phi) Other vector equations that can apply to this that I don't know maybe... 3. The attempt at a solution I figured that I try to find the vector B by doing the Pythagorean theorem with the two components of B and I get -12 as magnitude. After that I'm not even sure what to do, like for the 5(vector A) do I multiply the angle and magnitude by 5 then do the Vector A dot Vector B=abcos(phi) equation? Same question applies to b and how do I turn the magnitude and the angle into unit vector notation and magnitude angle notation? Thanks in advance. EDIT: Forget A, I solved it
The easiest way to do part b) is to start by finding [tex]A_x[/itex] and [tex]A_y[/itex]. As a hint on finding those components, consider [tex]\vec{A}\cdot\vec{e}_x[/itex] and [tex]\vec{A}\cdot\vec{e}_y[/itex]
 Where does the ex and ey come from?

Recognitions:
Homework Help

## Vectors dot product and cross product help

 Quote by maximade Where does the ex and ey come from?
I'm using them to represent the Cartesian unit vectors. You might be more used to seeing i and j....different authors use different notations for the same quantities, so it's worth familiarizing yourself with common notations.

 Tags components, cross product, dot product, trigonometry, vectors