证明:∵∠1+∠2=180°(已知),∠1+∠DFE=180°(邻补角定义),
∴∠2=∠DFE(同角的补角相等),
∴AB∥EF(内错角相等两直线平行),
∴∠3=∠ADE(两直线平行内错角相等),
又∠B=∠3(已知),
∴∠B=∠ADE(等量代换),
∴DE∥BC(同位角相等两直线平行),
∴∠C=∠AED(两直线平行同位角相等)
Sunday,June 1
Dear Tony,
Now we are having fun at Tian'anmen Square. The weather is fine. There are many people here. We'll visit the Bird's Nest and the Water Cube. In the evening,we'll have Beijing Duck. I love Beijing. I hope you will come to China soon.
Your friend,
Ben
Tony White__
78 Flower Road__
New York,CBE779D,USA
一人乘电梯上楼,在竖直上升过程中加速度a随时间t变化的图线如图所示,以竖直向上为a的正方向,则人对地板的压力( )