ｆ．３數第四彈

其實好simple：
只要不停咁find out D角，就可以做到呢條數：

a.) Let ∠CED=x, then ∠ABE=4x

Refer ABC is a st. line: ∠CBE=180-∠ABE=180-4x
Refer to △BCE, since BC=BE, therefore ∠BCE=∠BEC=[180-(180-4X)]/2=2x

Refer BCD is a st.line: ∠ECD=180-2x
Refer to △ECD, ∠CDE=180-∠CED-∠ECD=180-x-(180-2x)=x

Since ∠CED=∠CDE=x
Therefore, CE=CD

b.) 因為你叫只係做a 就得~如果你唔識先問我啦 ^o^