问题 解答题
已知:x:y:z=2:3:4,求:
(1)
x+2y
y
; 
(2)
3x
2x+3y-5z

(3)
x+2y+3z
3x-2y-z
答案

(1)∵x:y:z=2:3:4,

∴设x=2a,y=3a,z=4a,

x+2y
y
=
2a+6a
3a
=
8
3

(2)

3x
2x+3y-5z
=
3×2a
2×2a+3×3a-5×4a
=-
6
7

(3)

x+2y+3z
3x-2y-z
=
2a+2×3a+3×4a
6a-6a-4a
=-5.

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