MBA充分性判断a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3式子a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3 (1)abc≠0,且a²+b²+c²-ab-bc-ca=0(2)a+b+c=0答案说联合起来也不充分,可我怎么算不出
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![MBA充分性判断a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3式子a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3 (1)abc≠0,且a²+b²+c²-ab-bc-ca=0(2)a+b+c=0答案说联合起来也不充分,可我怎么算不出](/uploads/image/z/10165158-54-8.jpg?t=MBA%E5%85%85%E5%88%86%E6%80%A7%E5%88%A4%E6%96%ADa%281%2Fb%2B1%2Fc%29%2Bb%281%2Fa%2B1%2Fc%29%2Bc%281%2Fa%2B1%2Fb%29%E6%9C%89%E6%84%8F%E4%B9%89%E4%B8%94%E5%80%BC%E4%B8%BA-3%E5%BC%8F%E5%AD%90a%281%2Fb%2B1%2Fc%29%2Bb%281%2Fa%2B1%2Fc%29%2Bc%281%2Fa%2B1%2Fb%29%E6%9C%89%E6%84%8F%E4%B9%89%E4%B8%94%E5%80%BC%E4%B8%BA-3+%EF%BC%881%EF%BC%89abc%E2%89%A00%2C%E4%B8%94a%26sup2%3B%2Bb%26sup2%3B%2Bc%26sup2%3B-ab-bc-ca%3D0%EF%BC%882%EF%BC%89a%2Bb%2Bc%3D0%E7%AD%94%E6%A1%88%E8%AF%B4%E8%81%94%E5%90%88%E8%B5%B7%E6%9D%A5%E4%B9%9F%E4%B8%8D%E5%85%85%E5%88%86%2C%E5%8F%AF%E6%88%91%E6%80%8E%E4%B9%88%E7%AE%97%E4%B8%8D%E5%87%BA)
MBA充分性判断a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3式子a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3 (1)abc≠0,且a²+b²+c²-ab-bc-ca=0(2)a+b+c=0答案说联合起来也不充分,可我怎么算不出
MBA充分性判断a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3
式子a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3
(1)abc≠0,且a²+b²+c²-ab-bc-ca=0
(2)a+b+c=0
答案说联合起来也不充分,可我怎么算不出来.先拜过
我已经求得(1)、(2)单独都不充分,但是(1)(2)两个联合起来是否充分,我求不出来
MBA充分性判断a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3式子a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)有意义且值为-3 (1)abc≠0,且a²+b²+c²-ab-bc-ca=0(2)a+b+c=0答案说联合起来也不充分,可我怎么算不出
因为abc=/0
所以a,b,c肯定不为0
a*a+b*b+c*c=ab+ac+bc
(a+b+c)(a+b+c)=0
a*a+b*b+c*c+2ab+2ac+2bc=0
ab+ac+bc=0
a(1/b+1/c)+b(1/a+1/c)+c(1/a+1/b)=(a*a*b+a*c*c)/abc+(b*b*a+b*b*c)/abc+(c*c*a+c*c*b)/abc
约分一下就可以得到如下的
(a*b+a*c)/bc+(b*a+b*c)/ac+(c*A+c*b)/ab=(-bc)/bc+(-ac)/ac+(-ab)/ab=-3
不能保证分母有意义,所以不充分