已知集合 , . (1) 求; (2) 设集合 , 若 , 求b的取值范围. 答案:因为A={x|2x2−11x−21<0}={x|−32<x<7},B={x|−5<x≤1},所以∁RA=(−∞,−32]∪[7,+∞),(∁RA)∩B=(−5,−32].
C={y|−b≤y≤1−b},因为A∩C=C,所以C⊆A,则{−b>−32,1−b<7,解得−6<b<32,B的取值范围是(−6,32).
-Jack bought a new mobile phone the other day.-__________ ? That's his third one in just one month.
[ ]A. Had he B. Did he C. Does he D. Has he