已知x:y:z=3:4:7,且2x-y+z=-18,求式子x+2y-z的值.

问题描述:

已知x:y:z=3:4:7,且2x-y+z=-18,求式子x+2y-z的值.

因为x:y:z = 3:4:7
所以设 x = 3k ,y = 4k ,z = 7k
因为 2x - y + z = -18
所以 6k - 4k + 7k = -18
所以 k = -2
所以 x + 2y - z
= 3k + 8k - 7k
= 4k
= -8