limjunyoung
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5.甲不成立的命题是 x<=2且y>1 (1)
乙不成立的命题是x<3或y>=2 (2)
由1可以推2..而由2不能推到1
所以是 A
6.我觉得都对.
第一个可以由定义稍微变一下就能得到
第二个是垂心
第三个用向量计算可以得到
AP=AB+BP
3AP=3AB+3BP=AB+AC
3BP=AC-2AB=AC+2BA
AC=AB+BC=BC-BA 3BP=AC+2BA=BC-BA+2BA=BC+BA
第四个是三角外心的定义..如果是RT三角形.外心在第三边上(应该不算在三角形ABC内.)
钝角三角形外心在外面所以只能是锐角三角形
7.Since f(x) is the function on R,therefore we can assume that f(x+2) is non-zero,and hence
we multiply both side by f(x+2),which gives f(x)f(x+2)=-1 (1)
Substitute x+2 for x in the original equation,and we get f(x+2)f(x+4)=-1 (2)
Divide equation(2) by (1), it shows that f(x+4)/f(x)=1
again we assume f(x) to be non-zero and by rearranging the equation,we can deduce that
f(x+4)=f(x),which, by definition, is an aperiodic function with the least period 4.
Thus,I think that B gives the correct answer.
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