Answer
$\left( \cos 30\right) ^{2}-\left( \sin 30\right) ^{2}=\dfrac {1}{2}$
Work Step by Step
$\left( \cos \alpha \right) ^{2}-\left( \sin \alpha \right) ^{2}=\cos ^{2}\alpha \Rightarrow \left( \cos 30\right) ^{2}-\left( \sin 30\right) ^{2}=\cos \left( 2\times 30\right) =\cos 60=\dfrac {1}{2}$
