Chứng minh rằng tam giác ABF = tam giác ACE. Chứng minh FB = EC

$$\begin{gathered} \mathrm{Cho} ∆\mathrm{ABC} \mathrm{dựng} \mathrm{tam} \mathrm{giác} \mathrm{vuông} \mathrm{cân} \mathrm{BAE}; \widehat{\mathrm{BAE}}=90°, \\ \mathrm{B} \mathrm{và} \mathrm{E} \mathrm{nằm} \mathrm{ở} \mathrm{hai} \mathrm{nửa} \mathrm{mặt} \mathrm{phẳng} \mathrm{khác} \mathrm{nhau} \mathrm{bờ} \mathrm{AC}. \\ \mathrm{Dựng} \mathrm{tam} \mathrm{giác} \mathrm{vuông} \mathrm{cân} \mathrm{FAC}; \widehat{\mathrm{FAC}}=90°. \\ \mathrm{F} \mathrm{và} \mathrm{C} \mathrm{nằm} \mathrm{ở} \mathrm{hai} \mathrm{nửa} \mathrm{mặt} \mathrm{phẳng} \mathrm{khác} \mathrm{nhau} \mathrm{bờ} \mathrm{AB}. \\ \mathrm{a}) \mathrm{Chứng} \mathrm{minh} \mathrm{rằng}: ∆\mathrm{ABF} =∆\mathrm{ACE} \\ \mathrm{b}) \mathrm{FB}\perp \mathrm{EC} \end{gathered}$$