1991 年

In the figure, $\text{arc }AB:\text{arc }BC:\text{arc }CD:\text{arc }DE:\text{arc }EA=1:2:3:4:5$. Find $\theta$.

In the figure, $M$ is the mid-point of $BC$ and $AD=2DB$. $AM$ and $CD$ intersect at $K$. Find $\dfrac{\text{area of }\triangle ADK}{\text{area of }\triangle AKC}$.

In the figure, which of the pairs of triangles must be congruent?