1.设a b c∈R+,P=a+b-c Q=b+c-a R=c+a-b 则"PQR>0"是"P,Q,R同时大于零的?充分而不必要?必要而不充分?充分且必要?既不充分也不必要?2.已知二次函数f(x)的二次项系数为a,且不等式f(x)>0的解集(1,2)为若f(x)的
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![1.设a b c∈R+,P=a+b-c Q=b+c-a R=c+a-b 则](/uploads/image/z/14505009-33-9.jpg?t=1.%E8%AE%BEa+b+c%E2%88%88R%2B%2CP%3Da%2Bb-c+Q%3Db%2Bc-a+R%3Dc%2Ba-b+%E5%88%99%22PQR%3E0%22%E6%98%AF%22P%2CQ%2CR%E5%90%8C%E6%97%B6%E5%A4%A7%E4%BA%8E%E9%9B%B6%E7%9A%84%3F%E5%85%85%E5%88%86%E8%80%8C%E4%B8%8D%E5%BF%85%E8%A6%81%3F%E5%BF%85%E8%A6%81%E8%80%8C%E4%B8%8D%E5%85%85%E5%88%86%3F%E5%85%85%E5%88%86%E4%B8%94%E5%BF%85%E8%A6%81%3F%E6%97%A2%E4%B8%8D%E5%85%85%E5%88%86%E4%B9%9F%E4%B8%8D%E5%BF%85%E8%A6%81%3F2.%E5%B7%B2%E7%9F%A5%E4%BA%8C%E6%AC%A1%E5%87%BD%E6%95%B0f%28x%29%E7%9A%84%E4%BA%8C%E6%AC%A1%E9%A1%B9%E7%B3%BB%E6%95%B0%E4%B8%BAa%2C%E4%B8%94%E4%B8%8D%E7%AD%89%E5%BC%8Ff%28x%29%3E0%E7%9A%84%E8%A7%A3%E9%9B%86%281%2C2%29%E4%B8%BA%E8%8B%A5f%28x%29%E7%9A%84)
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