1. ## trig college question

Hey I need some help with this one.... I'm not to good with my trig rules.

The question is.

Let v = (-cos theta, sin theta)
w = (cos theta, -sin theta)

Find v.w.

Thanks heaps

2. Just a direct application of the dot/scalar product:
$\bold{v} \cdot \bold{w} = \left(\bold{v}_{i} \bold{w}_{i}\right) + \left(\bold{v}_{j} \bold{w}_{j}\right)$

where $\bold{v} = \left(-\cos \theta \right) \hat{\bold{i}} + \left(\sin \theta \right)\hat{\bold{j}}$ and $\bold{w} = \left(\cos \theta \right) \hat{\bold{i}} + \left(-\sin \theta \right)\hat{\bold{j}}$

Just plug and chug.