2003 年

In the figure, $XAB$ and $XDC$ are straight lines. If $DX=5$, $AX=6$ and $AB=4$, find $CD$.

In the figure, $BE$ and $BF$ are tangents to the circle at $A$ and $C$ respectively. If $\angle ADC=100^\circ$, then $\angle ABC=$

In the figure, $ABCD$ is a parallelogram and $ADH$, $EBC$ and $EFGH$ are straight lines. If $AD=6$, $DH=4$ and $EB:BC=3:4$, then $EF:GH=$

The circle $(x-4)^2+y^2=36$ intersects the positive $x$-axis and positive $y$-axis at $A$ and $B$ respectively. Find $AB$.