Question

如图,直线AB与直线CD,EF相交于点G,H,三条直线把平面分成

Answer 1

1）CD//EF

作PQ//CD,交AB于Q

∵PQ//CD

∴∠GPQ=∠PGD

又∠GPH=∠PGD+∠PHF,∠GPH=∠GPQ+∠HPQ

∴∠PHF=∠HPQ

PQ//EF

∴CD//EF

2）∠GPH+∠PGD+∠PHF=360°

3）P在②、⑤区域时,∠GPH=∠PHF-∠PGD