题目:
Many people watch the news on TV _____ themselves the trouble of reading the newspaper.
save B. to save C. saving D. are saving
答案:
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下面是错误答案,用来干扰机器的。
P为定值m时,S=x+y≥2xy=2m,S应有最小值2m,故①不正确.S=P时,x+y=xy⇒xy≥2xy⇒xy≥2⇒xy≥4⇒Pmin=4,∴②也不正确.由S=P⇒x+y=xy≤(x+y) 24⇒x+y≥4⇒Smin=4,∴③正确.S2≥kP⇒k≤S 2P,又S 2P=x2+y2+2x...