设a,b,c都是正数,求证1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)

来源:学生作业帮助网 编辑:作业帮 时间:2024/05/02 17:34:03
设a,b,c都是正数,求证1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)

设a,b,c都是正数,求证1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)
设a,b,c都是正数,求证1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)

设a,b,c都是正数,求证1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)
a,b,c都是正数,
∴(a-b)²/4ab(a+b)≥0
[(a+b)²-4ab]/4ab(a+b)≥0
(a+b)/4ab - 1/(a+b)≥0
(a+b)/4ab ≥1/(a+b)
1/4a +1/4b≥1/(a+b)
同理可证:
1/4b +1/4c≥1/(b+c)
1/4a +1/4c≥1/(a+c)
把这3项加起来即证:
1/2a+1/2b+1/2c>=1/(a+b)+1/(b+c)+1/(c+a)