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1. If x and y are integers and xy+x^2 is oddh which of the f

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1. If x and y are integers and xy+x^2 is oddh which of the following statements must be true?① x is odd② y is odd③ x+y is oddA. ①B. ③C. ① and ②D. ① and ③E. ② and ③2. For how many integers n is (2n+1)(3n-1) a negative number?A. NoneB. OneC. TwoD. ThreeE. Four求详解
1、x和y都是整数,“xy+x^2是奇数”就是说:x*(x+y)是奇数.
我觉得这道题问的是哪种组合是正确的.因为单独看,①②③都是推不出来的【也就是说A和B不对】,如果x是奇数,y也是奇数,那么x+y成了偶数,x*(x+y)也就成了偶数【所以C是不对的】,如果y和x+y都是奇数,那么x是偶数了,x*(x+y)也还是偶数【所以E也不对】,只有x和x+y都是奇数时,能证明x*(x+y)是奇数,所以D是正确答案.
2、要想让(2n+1)(3n-1)的值为负数,n有几种可能?
这道题是解不等式.根据题意,
要么是:2n+10
要么是:2n+1>0且3n-1