Question

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國一下數學 求解，拜託🥺

3
4
13. 已知x、y皆為正數,若
與
成正
x+2y 2x+y
比,當x=4時,y=6,則x=6時,y=?

Answer 1

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綾

正比是相除為定值
即[3/(x+2y)] / [4/(2x+y)] = k
已知x = 4時y = 6
代入得k = [3/(4+12)] / [4/(8+6)] = 21/32
x = 6代入
[3/(6+2y)] / [4/(12+y)] = 21/32
=> (36+3y) / (24+8y) = 21/32
=> (12+y) / (3+y) = 7/4
=> 48+4y = 21+7y
=> 3y = 27
=> y = 9

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