看起来没人问过gwd30-2^-^

谢沁薇

Q2:

The function f is defined for each positive three-digit integer n by f(n) = 2^x3^y5^z, where x, y and z are the hundreds, tens, and units digits of n, respectively.  If m and v are three-digit positive integers such that f(m) = 9f(v), then m-v = ?

 

A.    8

B.    9

C.    18

D.    20

                                  E.    80

下周二就考了。。。还在死命攻数学！ 谢谢

feier_79

f(v)=2^x3^y5^z

f(m)=2^x3^y+25^z

^v=100x+10y+z

^{m=100x+10(y+2)+z}

^m-v=20

谢沁薇

懂了！ 该敲脑袋
！

谢谢你

ilovecushi

以下是引用feier_79在2006-5-29 22:32:00的发言：

f(v)=2^x3^y5^z

f(m)=2^x3^y+25^z

^v=100x+10y+z

^{m=100x+10(y+2)+z}

^m-v=20

想请稳第二个式子是如何得出的呢?

crazecat123

以下是引用ilovecushi在2007-11-11 14:23:00的发言：

想请稳第二个式子是如何得出的呢?

f(m) = 9f(v)
       = 3^2 * f(v)
       = 3^2 * 2^x * 3^y * 5^z
       = 2^x * 3^(y+2) * 5^z

ilovecushi

i got it! thank u so much!