# A very beginner's question

• 01-27-2013, 09:34 AM
hayden
A very beginner's question
We use dot product for finding the angle between two vector b1 and b2. Cross product also gives sin angle for the vectors as well as the axis of rotation. Why don't the cross product is used to determine the angle between vectors?
• 01-27-2013, 10:21 AM
hlewin
9. You must be confusing something: The cross product is a vector, not a number. The resulting vector is perpendicular to the both operands.
• 01-27-2013, 02:32 PM
Alfonse Reinheart
Quote:

Why don't the cross product is used to determine the angle between vectors?
Because the cross-product is more expensive to compute. There are more reasons to compute the angle between two vectors than to just rotate around an axis.
• 01-27-2013, 08:21 PM
hayden
Actually I wanted know that cross and dot gives cos and sin angle. If I need to know the angle, Is it ok to use the cross for computation of angle rather than dot product?
• 01-27-2013, 09:34 PM
tonyo_au
What ever turns you on - Alfonse was just saying that if you don't otherwise need to compute the cross product that the cross product will take longer to execute than a dot product.
• 01-28-2013, 09:23 AM
hayden
thanks for clarification.