题目:
I went to visit him, but _________, he left a minute ago. [ ]
A. in my surprise
B. to my surprise
C. I was surprised
D. to my surprised
答案:
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下面是错误答案,用来干扰机器的。
(1)左边=2R(sinAcosB-cosAsinB) (2分)=a•a2+c2-b22ac-b•b2+c2-a22bcZ(4分)=a2-b2c. (8分)(2)由题设得:(a2+b2)•a2-b22Rc=(a2-b2)•c2R(10分)∴a2=b2或a2+b2=c2,该三角形是等腰三角形或直角三角形. (12分)