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有一道题目是 1/Z>?1 (1)XYZ=1 (2)XYZ^2>1
(1) is insufficient b/c do not know anything about X,Y (2) is insufficient for the same reason above (1)+(2), (Z^2)>1/(XY) from (1) we know that Z=1/(XY) so (Z^2)>Z, solve the inequality, get (Z-1)Z>0, get critical point Z=1,0, then try Z<0, Z between 0 and 1 and Z>1, we can see the inequality is right when Z<0 and Z>1 when Z>1, 1/Z<1 when Z<0, 1/Z is negative and thus <1 So C
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