✔ 最佳答案
1. -10.5077 (沒算錯的話...)
https://www.flickr.com/photos/25446201@N08/15109813904/
2. 10×2^n≧4×10^6
2^n≧ 2^2 ×10^5
2^ (n-2) ≧10^5
(n-2) log 2≧5
n-2≧16.6
n≧18.6 取整數為19
=>1980+19 =1999年
3. log_A B+log_A C +log_B C+log_B A+log_C B+logC A
= log B-log A+log C-log A+log C-log B+log A-log B+ log B-log C+ log A -logC=0
4. 2log(X-2Y) =logX+logY
log (X-2Y)^2 = log XY
X^2-4XY+4Y^2=XY
X^2-5XY+4Y^2 =0
(X-4Y)(X-Y)=0
X=Y => X-2Y= -Y <0 不合
X=4Y => X/2Y=4Y/2Y=2
5.
log M= 7.... => M=a×10^7 ,1≦a < 10
√M=√(a×10^7) =√(0.1a) ×10^4= a* ×10^4, 0.316...≦a*<1
1/√M= 1/(a* ×10^4) = a** ×10^-4 , 1<a**≦3.16....
log (1/√M ) = -4+ log a** , 0< log a** ≦0.5003....
=> -4 < log (1/√M )≦-3.499...
首數為-3
6.
(log_2 5+log_4 0.2)×(log_5 2+log_25 0.5)
=(log 5- log 2 + log 0.2- log 4)×(log 2-log 5+log 0.5 -log 25)
=(log 5- log 2+log2 -1-2log 2)×(log 2 - log 5 +log 5 - l -2 log 5)
=(log 5 - log 2 -1) ×( -2 log 5 + log 2 -1)
=(log 5 - log 2 -log 5 -log 2) × ( -2 log 5 + log 2 -log 5 -log 2)
=(-2 log 2 )× (-3 log 5)
=6 log 2 × log 5
=6×0.3010×(1-0.3010)=1.262394≒1.2624
7. log_A B =X
log_A 1/B^(1/5) = log_A B^(-1/5)=(-1/5) log_A B =(-1/5) X
8. log[log_1/2 (log_1/3 X) ]有意義
=> log_1/2 (log_1/3 X) >0
=>(log_1/3 X)>1
=> X >1/3
9. log_1/2 (X-1)>log_1/4 (2X+1)
log (X-1) -log (1/2) > log (2x+1) - (log 1/4) = log (2x+1) - 2(log 1/2)
log (X-1) - log (2x+1) > -(log 1/2)
log { (x-1)/(2x+1) } > log 2
(x-1)/ (2x+1) > 2
x-1> 2 (2x+1) = 4x+2
-3 > 3x
x<-1
10. 題目有疑問?
若為(X^2)( logX) =10X
log X = 10/X 只有一個解
若為X^(2 logX) =10X
(2 logX) (logX ) =1+log X
2 (log X) ^2 - logX -1 =0
(2 log X +1) (log X -1)=0
log X = -1/2 or 1
X = 1/√10 or 10
X1X2=10×1/√10=√10
11.
log 678 = log (6.78×10^2) = 2+ log 6.78........ 首數 2
log 12.3 = log (1.23 ×10) = 1+ log 1.23 ..........尾數log 1.23
= >log X =首數+尾數 =2+ log 1.23 =log 100 +log 1.23 =( log 100×1.23)=log 123
= >X=123
12.
2^X =5^(1-X)
X ln 2 =(1-X) ln 5 =(1-X) - (1-X) ln 2
ln 2= 1-X
X= 1-ln2 =1-0.3010 =0.6990