Construct the right triangle $PQR$ whose perpendicular sides are $4.5 \mathrm{cm}$ and $6 \mathrm{cm}$. Also locate its circumcentre and draw the circumcircle.

$ABCD$ is a square, diagonals $AC$ and $BD$ meet at $O$. The number of pairs of congruent triangles with vertex $O$ are

In the figure, $O$ is the centre of the circle and $\angle ACB=40°$ then $\angle AOB=$

In a cyclic quadrilateral $ABCD, \angle A=4x, \angle C=2x$ the value of $x$ is

In the figure, $O$ is the centre of a circle and diameter $AB$ bisects the chord $CD$ at a point $E$ such that $CE=ED=8 \mathrm{cm}$ and $EB=4 \mathrm{cm}$. The radius of the circle is

In the figure, $PQRS$ and $PTVS$ are two cyclic quadrilaterals, If $\angle QRS=100°$, then $\angle TVS=$