S.2數學題幫幫手~!!

🎓 學業台教學

ERIC

2009-03-28 9:26 pm

9^(x+2)=36

求3^x =

請幫幫手...thanks!!

回答 (3)

用戶2053

2009-03-28 11:34 pm

✔ 最佳答案

9^(x+2)=36
3^2(x+2) = 36
3^(2x+4) = 36
3^2x * 3^4 = 36
3^2x = 36 / (3^4)
(3^x)^2 = 4/9
3^x = √(4/9)
3^x = 2/3

2009-03-28 15:43:32 補充：
方法二 :

9^(x+2)=36

[3^(x+2)] ^ 2 = 6^2 (由於3^(x+2)不會是負數,下一步等式兩邊取正數)

3^(x+2) = 6

3^x * 3^2 = 6

3^x = 2/3

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