幾何與角

In the figure, $ADB$, $BEC$ and $CFA$ are straight lines. If the area of $\triangle ABC$ is $225\text{ cm}^2$, find the area of the parallelogram $DECF$.

In the figure, $ABCD$ and $AGFE$ are straight lines. Find $CF$.

In the figure, $ABCD$ is a parallelogram. Find $\angle BDE$.

In the figure, $O$ is the centre of the circle. $EAOB$ and $EDC$ are straight lines. Find $x$.

In the figure, $AB=CD$, $\angle CAB=\angle ECD$ and $\angle ABC=\angle CDE$. Which of the following must be true? I. $\triangle ABC\cong\triangle CDE$ II. $\triangle ABC\sim\triangle EAC$ III. $EAC$ is an isosceles triangle

In the figure, $AB$ is tangent to the circle at $B$. Find $\angle DCE$.

In the figure, $\overset{\frown}{AB}:\overset{\frown}{BC}:\overset{\frown}{CD}=2:1:3$. Find $\angle ADC$.

In the figure, $AEC$ and $BED$ are straight lines. If the area of $\triangle ABE=4\text{ cm}^2$ and the area of $\triangle BCE=5\text{ cm}^2$, find the area of $\triangle CDE$.

In the figure, $O$ is the centre of the circle. Find $x$.

In the figure, $AB$ is a diameter of the circle. Find $x$.