Question

将纸片沿EF折叠,当点A落至点A1处,当点A1在△ABC的内部时,试猜想并证明∠BEA1+∠CFA1与∠A的关系

Answer 1

∠B+∠C=180°-∠A

∠A=∠A1=40°

所以∠B+∠C=140

∠BEF+∠CFE=360-∠B-∠C=220

∠BEA1+∠CFA1=∠BEF+∠CFE-∠A1EF-∠A1FE

∠A1EF+∠A1FE=180-∠A1=140

所以∠BEA1+∠CFA1=220-140=80°百度地图