Trigonometric Values?

Geometry Level 4

$\large \ \cos^{2} 73^{\circ} \ + \ \cos^{2} 47^{\circ} \ + \ \cos 73^{\circ} \cos 47^{\circ}$

If the value of the above expression is equal to $\dfrac {a}{b}$ , where $a$ and $b$ are coprime positive integers, find $a+b$ .