问题
选择题
△ABC中，已知其面积为S=
|
答案
∵cosC=
，即a2+b2-c2=2abcosC，S=a2+b2-c2 2ab
absinC，且S=1 2
（a2+b2-c2），1 4
∴
absinC=1 2
abcosC，即tanC=1，1 2
∵C为三角形的内角，
∴C=45°．
故选B
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△ABC中，已知其面积为S=
|
∵cosC=
，即a2+b2-c2=2abcosC，S=a2+b2-c2 2ab
absinC，且S=1 2
（a2+b2-c2），1 4
∴
absinC=1 2
abcosC，即tanC=1，1 2
∵C为三角形的内角，
∴C=45°．
故选B
选词填空（共10小题，每小题1分，满分10分）
小题1:If there is any new word, you can __________ your dictionary. 小题2: I __________ go fishing than swimming. 小题3:We can ___________ whatever information on the Internet. 小题4: Though ____________ only rice and muskets, our army won the war. 小题5: __________ his friends’ support, the poor student was able to finish university. 小题6:She is____________________ hearing from her boyfriend in Australia. 小题7: On the Dragon Boat Festival people usually eat zongzi__________Qu Yuan,a great poet. 小题8: What he said ___________ me _________ my father, he once told me like that 小题9: — How did you find this important letter? — Quite ________. 小题10:He has been asked to ________ his absence. |