Aptitude - Logarithm - Discussion
Discussion Forum : Logarithm - General Questions (Q.No. 12)
12.
| If logx |  |
9 |  |
= - | 1 | , then x is equal to: |
| 16 | 2 |
Answer: Option
Explanation:
| logx | |
9 | |
= - | 1 |
| 16 | 2 |
 x-1/2 |
= | 9 |
| 16 |
| |
1 | = | 9 |
| x | 16 |
| x = |
16 |
| 9 |
| x = |
|
16 | |
2 |
| 9 |
| x = |
256 |
| 81 |
Discussion:
17 comments Page 1 of 2.
Rohit said:
1 decade ago
loga(9/16)=-1/2
log(9/16)/loga=-1/2
2log(9/16)=-loga
log(81/256)=log(1/a)
a=256/81
log(9/16)/loga=-1/2
2log(9/16)=-loga
log(81/256)=log(1/a)
a=256/81
(1)
JOSHUA said:
1 decade ago
You must cross multiply at the third, why reciprocating at that place?
Malathi said:
1 decade ago
I can't understand.
Carbon said:
1 decade ago
A far better solution can be done just by observation,
Just multiply both side by -(1/2) to make RHS.
Then simplifying LHS we get,
Logx(9/16) pow(-1/2).
= logx(256/81) = 1.
Thus,
X=256/81.
Just multiply both side by -(1/2) to make RHS.
Then simplifying LHS we get,
Logx(9/16) pow(-1/2).
= logx(256/81) = 1.
Thus,
X=256/81.
(1)
Keerthi said:
1 decade ago
While multiplying both sides by - (1/2) RHS becomes 1/4. How come 1? I can't understand.
Sushant said:
1 decade ago
Multiplying both side by -2 we get,
-2Logx(9/16) = 1.
Logx(256/81) = 1.
x pow 1 = 256/81.
x = 256/81.
-2Logx(9/16) = 1.
Logx(256/81) = 1.
x pow 1 = 256/81.
x = 256/81.
Jai said:
10 years ago
I can't get that clearly, please some one explain me short & sweetly.
PAVITHRA_228 said:
10 years ago
As per the formula.
log x = m.
=> log x/log a = m.
=> log (9/16)/log a = -1/2.
=>2 log (9/16) = -log a.
=> log (9/16)^2 = log(1/a).
=> log (81/256) = log(1/a).
log gets cancelled,
=> a = 256/81.
log x = m.
=> log x/log a = m.
=> log (9/16)/log a = -1/2.
=>2 log (9/16) = -log a.
=> log (9/16)^2 = log(1/a).
=> log (81/256) = log(1/a).
log gets cancelled,
=> a = 256/81.
(2)
Kathir said:
9 years ago
@Rohit. Good explanation.
Mounika said:
9 years ago
If logx (0.1) = -1/3, then the value of x is.
Please tell me the answer for this.
Please tell me the answer for this.
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