Two sides of a triangle are $9$ cm and $10$ cm with included angle $60°$. Its area is —

Using $\frac{1}{2}ab\sin C = \frac{1}{2}\cdot 9 \cdot 10 \cdot \sin 60° = 45 \cdot \frac{\sqrt{3}}{2} = \frac{45\sqrt{3}}{2}$ sq cm. The value produces the radical.