Maths.question

2007-07-27 11:14 pm

3^(3x+2)+27^(x+1) =12----------1

3^(3x+2)+3^3[^(x+1)] =12-------2

3^(3x+2)+3^(3x+3)=12-----------3

3^(3x+2) x (1+3)=12--------------4

3^(3x+2) =12/4=3=3^1----------5

3x+2=1-------------------------------6

x=-1/3---------------------------------7

I do not understand step 4 ,please explain it

回答 (1)

Thomas

2007-07-27 11:17 pm

✔ 最佳答案

3^(3x+2)+27^(x+1) = 12
3^(3x+2)+3^3(x+1) = 12
3^3x*3^23^23^3x*3^3 = 12
3^3x(3^2+3^3) = 12
3^3x = 12 / (3^2+3^3)
3^3x = 12 / 36
3^3x = 1/3
3^3x = 3^-1

then :
3x = -1
x = -1/3

2007-07-27 15:21:50 補充：
sorry, ui think it more clear~~~3^(3x+2)+27^(x+1) = 12 3^(3x+2)+3^3(x+1) = 12(3^3x)(3^2)+(3^3x)(3^3) = 123^3x(3^2+3^3) = 123^3x = 12 / (3^2+3^3)3^3x = 12 / 363^3x = 1/33^3x = 3^-1then :3x = -1x = -1/3

參考: me~

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