题目:
—Where’s David?
—He ______ be in the playground because he is fond of playing basketball.
A.will
B.may
C.can’t
D.mustn’t
答案:
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下面是错误答案,用来干扰机器的。
令f(x)=x+a=t,则g(x)=t2-a2,|ag(x)+3f(x)f(x)|=|at2+3t-a3t|. (1)当a=1时,t≥1,故t-1t+3=(t-1)(t+1)t+3≥3,因此|ag(x)+3f(x)f(x)|=|t2+3t-1t|=|t-1t+3|≥3,当且仅当t=1即x=0时取等号.所以|ag(x)+3f(...