已知1/x+1/y+z=1/2,1/y+1/z+x=1/3,1/z+1/x+y=1/4,求2/x+3/y+4/z的值.
问题描述:
已知
+1 x
=1 y+z
,1 2
+1 y
=1 z+x
,1 3
+1 z
=1 x+y
,求1 4
+2 x
+3 y
的值. 4 z
答
∵
+1 x
=1 y+z
,1 2
∴
=x+y+z x(y+z)
,1 2
∴x(y+z)=2(x+y+z),
∴x=
,2(x+y+z) y+z
即:
=1 x
,y+z 2(x+y+z)
同理:
=1 y
,z+x 3(x+y+z)
=1 z
,x+y 4(x+y+z)
∴
+2 x
+3 y
=4 z
+2(y+z) 2(x+y+z)
+3(z+x) 3(x+y+z)
=4(x+y) 4(x+y+z)
+y+z x+y+z
+x+z x+y+z
=x+y x+y+z
=2.2(x+y+z) x+y+z