已知a,b,c∈R,a+b+c=0,abc<0求证:1⼀a+1⼀b+1⼀c>0

2025-02-27 01:23:14
推荐回答(1个)
回答1:

证明:因为a+b+c=0,则b=-(a+c), 1/a+1/b+1/c =(bc+ac+ab)/abc =[(a+c)b+ac]/abc =[-(a+c)(a+c)+ac]/abc =-(a^2+ac+c^2)/abc =-[(a+c/2)^2+c^2*(3/4)]/abc, 因为-[(a+c1/2)^2+c^2*(3/4)]<0,abc<0, 所以-[(a+c/2)^2+c^2*(3/4)]/abc>0, 即1/a+1/b+1/c>0。