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
Just a direct application of the dot/scalar product:
$\displaystyle \bold{v} \cdot \bold{w} = \left(\bold{v}_{i} \bold{w}_{i}\right) + \left(\bold{v}_{j} \bold{w}_{j}\right)$
where $\displaystyle \bold{v} = \left(-\cos \theta \right) \hat{\bold{i}} + \left(\sin \theta \right)\hat{\bold{j}}$ and $\displaystyle \bold{w} = \left(\cos \theta \right) \hat{\bold{i}} + \left(-\sin \theta \right)\hat{\bold{j}}$
Just plug and chug.