题目

已知在四边形ABCD中，∠A=∠B=90°． （1）∠ABC+∠ADC=180°； （2）如图①，若DE平分∠ADC，BF平分∠ABC的外角，请写出DE与BF的位置关系，并证明； （3）如图②，若BE，DE分别四等分∠ABC、∠ADC的外角（即∠CDE=∠CDN，∠CBE=∠CBM），试求∠E的度数      答案：       （1）解：∵∠A=∠C=90°， ∴∠ABC+∠ADC=360°﹣90°×2=180°； 故答案为：180°； （2）解：延长DE交BF于G， ∵DE平分∠ADC，BF平分∠CBM， ∴∠CDE=∠ADC，∠CBF=∠CBM， 又∵∠CBM=180°﹣∠ABC=180°﹣（180°﹣∠ADC）=∠ADC， ∴∠CDE=∠CBF， 又∵∠BED=∠CDE+∠C=∠CBF+∠BGE， ∴∠BGE=∠C=90°， ∴DG⊥BF， 即DE⊥BF；第一节 根据提示，用单词的适当形式填空【1】Our government is making preparation in case a new situation .(出现)【2】Bob was quite ________ (幽默), and I liked that about him.【3】Personally speaking, I a great importance to reading widely.【4】It’s a disease which ________ (影响)mainly older people.【5】She wanted to be the first woman to climb Mount Qomolangma, and she almost _____.(成功)【6】According to laws, the children under ten are not allowed to be e as workers in a factory.【7】It was such a r to hear that Martha was found safe and well.【8】My g________ is to study hard, get a good job and support my family.【9】Whales are still being h and killed in the Arctic.【10】After years of hard work, his dream has become a r________ .