①齐桓公 ②晋文公 ③秦孝公 ④楚庄王
A:①②④
B:②③④
C:①③④
D:①②③④
伽利略斜面实验中:
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若ai,bi∈R+i=1,2,3,...,n ,求证a1b1+···+anbna1b1+···+anbn≥a1+···+an2 .
图一是____;图二是____