1) 7 ^ ( 2x - 5 ) = 15 ^ ( 1 - x)
2) 2 * 3 ^ ( x + 3 ) + 7 * 3 ^( x - 2 ) = 493
解答者請寫清楚計算過程,謝謝.
兩題數學解方程題目
2008-02-16 6:58 am
回答 (2)
2008-02-16 7:11 am
✔ 最佳答案
7^(2x-5)=15^(1-x)(2x-5) log 7 = (1-x) log 15
(2log7)x - 5log7 = log15 - (log15)x
(log49)x - log35 = log15 - (log15)x
(log49+log35)x=log15+log35
(log1715)x=log525
x=log1715/log525
x=1.1890 (準確至小數後四位)
2)
2*3^(x+3)+7*3^(x-2)=493
3^(x-2)[2*(3^5)+7]=493
3^(x-2)(493)=493
3^(x-2)=1
x-2=0
x=2
2008-02-17 10:14 pm
1)
7^(2x-5)=15^(1-x)
(2x-5) log 7 = (1-x) log 15
(2log7)x - 5log7 = log15 - (log15)x
(log49)x - log35 = log15 - (log15)x
(log49+log35)x=log15 +log35
(log1715)x=log525
x=log1715/log525
x=1.1890 (準確至小數後四位)
2)
2*3^(x+3)+7*3^(x-2)=493
3^(x-2)[2*(3^5)+7]=493
3^(x-2)(493)=493
3^(x-2)=1
x-2=0
x=2
7^(2x-5)=15^(1-x)
(2x-5) log 7 = (1-x) log 15
(2log7)x - 5log7 = log15 - (log15)x
(log49)x - log35 = log15 - (log15)x
(log49+log35)x=log15 +log35
(log1715)x=log525
x=log1715/log525
x=1.1890 (準確至小數後四位)
2)
2*3^(x+3)+7*3^(x-2)=493
3^(x-2)[2*(3^5)+7]=493
3^(x-2)(493)=493
3^(x-2)=1
x-2=0
x=2
收錄日期: 2021-04-25 21:29:31
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