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Given in the△ABC,a,b,c are three sides of the triangle,and 3a=2b+1c,then∠A is（ ） （英汉
题目详情
Given in the△ABC,a,b,c are three sides of the triangle,and 3a=2b+1c,then∠A is（ ） （英汉
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答案和解析
若a是最大边则,a＞b a＞c 所以 1a＜ 1b,1a＜ 1c,
∴ 1a+ 1a+ 1a＜ 1b+ 1b+ 1c,
∴ 3a＜ 2b+ 1c 而 3a=2b+1c,
所以矛盾所以a不是最大边,若是∠A是钝角或直角则a是最大边与a不是最大边矛盾所以∠A是锐角；
故选：A．
∴ 1a+ 1a+ 1a＜ 1b+ 1b+ 1c,
∴ 3a＜ 2b+ 1c 而 3a=2b+1c,
所以矛盾所以a不是最大边,若是∠A是钝角或直角则a是最大边与a不是最大边矛盾所以∠A是锐角；
故选：A．
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