數題數學題 - Ans.fyi 參考答案

數題數學題

[匿名]

2010-01-11 10:22 am

1. find x 9(3^(x+1)) = 27^2x
2. A researcher investigated the growth of a certain bacteria in a laboratory. He found that the number(N) of bacteria after (t) hours is given by N=1000(1.24^2t). How many bacteria are there initially?
3. The energy released as seismic waves in the earthquakes in city A and city B are 6.78 * (10^9) Joules and 2.43 * (10^11) Joules respectively. Find the difference in magnitudes of the two earthquakes on the Richter scale.(用1式2式)
4. 2logx + log5(1/x^2)
p.s (5)是底

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回答 (1)

kent

2010-01-11 7:06 pm

✔ 最佳答案

1.) 9(3^(x+1)) = 27^2x
3^2(3^(x+1))=3^3(2x)
3^(2+x+1)=3^6x
x+3=6x
5x=3
x=3/5
2.) bacteria are there initially is when t=0
N=1000(1.24^2t)
N=1000(1.24^2(0))
N=1000(1.24^0)
N=1000(1)
N=1000
3.) difference in magnitudes of the two earthquakes
=[log (2.43 * (10^11))]/[log(6.78 * (10^9))]
=1.158
4.) 2logx + log5(1/x^2)
=2logx + log5/x^2
=2logx + log5 - logx^2
=2logx + log5 - 2logx
=log5
=0.699

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