# Thread: proving this physics problem?

1. ## proving this physics problem?

The information that was given to me was the following:

The following are all vectors:
a, b, c, d

k = (a+b) (c+d)

prove: k = (a x c) + (a x d) + (b x c) + (b x d)

Any help would be appreciated. Thanks!

2. Originally Posted by colerelm1
The information that was given to me was the following:

The following are all vectors:
a, b, c, d

k = (a+b) x (c+d) Mr F says: I assume the important red product was missing ....?

prove: k = (a x c) + (a x d) + (b x c) + (b x d)

Any help would be appreciated. Thanks!
Google: cross product distributive proof

3. ## Dot product

What if I mean to say " k = (a + b) . (c + d)"

meaning dot product

Does this make a difference from what you had said?

4. Originally Posted by colerelm1
What if I mean to say " k = (a + b) . (c + d)"

meaning dot product

Does this make a difference from what you had said?
sure would ... $k = (a \times c) + (a \times d) + (b \times c) + (b \times d)$ is a vector

$(a + b) \cdot (c + d)$ is scalar.