# Thread: I don't understand a step in this proof. (Space vectors topic)

1. ## I don't understand a step in this proof. (Space vectors topic)

The proof I am doing is #7 of the attached pdf.

For the following (formatting is off from the copy pasting so look at the pdf):
a2 × b = |a2| |b| sin f n = |a| sin q |b| n = |a| |b| sin q n = a × b

How do I go from |a2||b|sin(phi) n to |a| sin(theta)|b| n? It seems that there is an important reason for this step because I would of skipped directly to |a||b|sin(theta)n. Is there something I should not assume that I am assuming? Whether, it is okay for me to skip this step or not, what is going on in the step I would of skipped?

Any input would be appreciated.

2. ## Re: I don't understand a step in this proof. (Space vectors topic)

Originally Posted by s3a
The proof I am doing is #7 of the attached pdf.
For the following (formatting is off from the copy pasting so look at the pdf):
a2 × b = |a2| |b| sin f n = |a| sin q |b| n = |a| |b| sin q n = a × b

How do I go from |a2||b|sin(phi) n to |a| sin(theta)|b| n? It seems that there is an important reason for this step because I would of skipped directly to |a||b|sin(theta)n. Is there something I should not assume that I am assuming? Whether, it is okay for me to skip this step or not, what is going on in the step I would of skipped?

Any input would be appreciated.