# Dot product of two vectors

1. Jul 18, 2012

### amaresh92

greetings,
consider two vector as it is A(1,0) and B(-1,0). now if we find the projection of A on B we should get zero but its coming -1.where i am going wrong?
advanced thanks.

2. Jul 18, 2012

### Ibix

What's the condition for dot products to be zero?

3. Jul 18, 2012

### I like Serena

Hi amaresh92!

You're not going wrong.
The projection is not supposed to come out as zero, since the vectors are opposite.

Repeating Ibix, do you know what it means if the projection is zero?

4. Jul 19, 2012

### amaresh92

what i have understood is we find projection of one vector to another when we need to find the magnitude of one vector in the direction given by another vector.

if its wrong then what is dot product and projections are ?

any help will be appreciated
thanks

5. Jul 19, 2012

### Ibix

Your understanding appears to be correct. Your application to this particular problem is wrong.

Your vector A points due East. Which way is B pointing? How far in an easterly direction is that, ignoring any northerly or southerly motion?

6. Jul 19, 2012

### I like Serena

The dot product and projection are zero if and only if the vectors are perpendicular.

Opposite vectors are not perpendicular - they are in the same (but opposite) direction.

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