Originally Posted by

**Mr Rayon** $\displaystyle u = 3i + 3j $and $\displaystyle v = 6i + 2j$

$\displaystyle

\left | u \right | = \sqrt{3^2 + 3^2} = \sqrt{18} = 3\sqrt{2}

\left | v \right | = \sqrt{6^2 + 2^2} = \sqrt{40} = 2\sqrt{10}

$

Okay, I've drawn a diagram...and then I find the difference between the angles:

$\displaystyle cos \theta = \frac{3}{3\sqrt{2}}

$, $\displaystyle cos \theta = \frac{3\sqrt{2}}{6} = \frac{\sqrt{2}}{2}

$

$\displaystyle cos\theta = \frac{6}{2\sqrt{10}}$, $\displaystyle cos\theta = \frac{6\sqrt{10}}{20} = \frac{3\sqrt{10}}{10}$

$\displaystyle \frac{3\sqrt{10}}{10} - \frac{5sqrt{2}}{10}$

$\displaystyle u\cdot v = \left |u \right | \left | v \right |cos\theta$

I am lost from here, and is the above right? Can somebody provide complete working out?

EDIT: I don't know what I'm doing here.