解： 请结合图形 看解答 取 过D作DE⊥AC ，现在证明AE与AD的夹角就是AD与平面ABC的夹角 即证明 DE是垂直与平面ABC 因为 AD⊥平面ADC 所以 AD⊥BC 又 角BCD=90° ==> BC⊥CD BC⊥CD 且 BC⊥AD 所以 BC⊥平面ADC 由 BC⊥平面ADC 得到 BC⊥DE ………………（1） DE⊥AC DE⊥BC ==》 DE⊥平面ABC 那么 AD与平面ABC的夹角就是 角DAE tanA=DC/AD=1/2

Life in the future As time goes by, there are going to be big changes in our everyday lives in the future. For example, As time goes by, there are going to be big changes in our everyday life. For example, when we are hungry, we don't need to cook in a hurry. Just take some pills, and everything will be OK. When we are free, we can go anywhere by spacecraft. It will be very cheap, just like taking a taxi now. And of course, if we want to see what is like under the sea, just travel down there in a flying object like UFO. Maybe there will be a lot of cities and people living there. I think it'll be very easy to travel anywhere, not only in our world, but also in space and in the deep sea.