[問題]GWD-5-19

[Grace]

Q19:
If 5x – 5x - 3 = (124)(5y), what is y in terms of x?

A. X
B. x - 6
C. x - 3
D. 2x + 3
E. 2x + 6

Ans: C

5x – 5x - 3 ＝5^x-5^(x-3)/5^3=5^x*(125-1)/125=5^x*124/125= (124)(5y)--->5^x=5^3*5^y=5^(3+y)--->x=3+y-->y=x-3--->答案是C

我看不懂CD解法, HELP~ :o

[homaru]

If 5[sup]x[/sup] – 5[sup]x-3[/sup] = (124)(5[sup]y[/sup]), what is y in terms of x?

5[sup]x[/sup] – 5[sup]x-3[/sup]
=(5[sup]3[/sup])*5[sup]x-3[/sup] - 5[sup]x-3[/sup]
=125*5[sup]x-3[/sup] - 5[sup]x-3[/sup]
=124*5[sup]x-3[/sup]=(124)(5[sup]y[/sup])

so y=x-3

ps. 從word上貼來的題目,指數(次方)的部分會改變或消失,要自己用上面"Sup"的按鈕來加上指數

[Grace]

First of all, thanks for your sooneset response and thanks for
the reminder.

我不懂為什麼 要乘上5^3????
Help~ Thanks in advance.

[huacy]

First of all, thanks for your sooneset response and thanks for
the reminder.

我不懂為什麼 要乘上5^3????
Help~ Thanks in advance.

這樣才方便湊成 5[sup]y[/sup] (5[sup]x[/sup]=5[sup]3[/sup]*5[sup]x-3[/sup])
然後等號左右邊比對一下 就可以得知 y=x-3

[homaru]

(5^3)*[5^(x-3)]=5^(3+x-3)=5^x
指數相加的觀念

[Grace]

謝謝huacy站大及homaru的解釋...我懂了...
I appreciate your help~