The perimeter of equilateral $\Delta ABC$ is $30$. Find its area. (in $\sqrt{3}$)

Prove that the area of the equilateral triangle drawn on the hypotenuse of a right-angled triangle is equal to the sum of the areas of the equilateral triangles drawn on the other two sides of the triangle.

For the correspondence $ABC \leftrightarrow RPQ$ between $\Delta ABC$ and $\Delta PQR$,$\angle B$ corresponds to $\ldots \ldots \ldots \ldots$

In $\Delta ABC$,$m \angle B = 90^{\circ}$ and $m \angle C = 30^{\circ}$. If $AC = 10$,then $AB = \ldots$

In $\Delta XYZ,$ the bisector of $\angle X$ intersects $\overline{YZ}$ at $T$. If $XY = 10, XZ = 14$ and $YT = 5,$ find $YZ.$

In $\Delta ABC$,$m \angle B = 90^{\circ}$ and $\overline{BD}$ is an altitude to the hypotenuse $\overline{AC}$. Then,the correspondence $ABC \leftrightarrow \ldots$ between $\Delta ABC$ and $\Delta ADB$ is a similarity.