已知自然数a,b,c,满足a2+b2+c2+42<4a+4b+12c和a2-a-2>0,则代数式1/a+1/b+1/c的值是 _.
问题描述:
已知自然数a,b,c,满足a2+b2+c2+42<4a+4b+12c和a2-a-2>0,则代数式
+1 a
+1 b
的值是 ______. 1 c
答
∵a2-a-2>0,(a-2)(a+1)>0,∴a>2或a<-1.
a2+b2+c2+42-4a-4b-12c<0
配方得:(a-2)2+(b-2)2+(c-6)2<2,
∵a,b,c是自然数,∴a=3,b=2,c=6,
∴
+1 a
+1 b
=1 c
+1 3
+1 2
=1 6
+2 6
+3 6
=1.1 6
故答案是:1.