If log โก 10 5 + log โก 10 ( 5 ๐ฅ + 1 ) = log โก 10 ( ๐ฅ + 5 ) + 1 log 10 โ 5+log 10 โ (5x+1)=log 10 โ (x+5)+1, find ๐ฅ x.
Aptitude
Logarithm
Difficulty: Medium
Choose an option
-
A2
-
B3
-
C4
-
D5
Answer
Correct Answer: 3
Explanation
Given data & domain
- 5x+1 > 0, x+5 > 0 (log arguments must be positive).
Concept / Approach
- Use log properties: log โก ๐ + log โก ๐ = log โก ( ๐ ๐ ) loga+logb=log(ab) and 1 = log โก 10 10 1=log 10 โ 10.
Step-by-step calculation log โก 10 [ 5 ( 5 ๐ฅ + 1 ) ] = log โก 10 [ 10 ( ๐ฅ + 5 ) ] log 10 โ [5(5x+1)]=log 10 โ [10(x+5)] โ 25 ๐ฅ + 5 = 10 ๐ฅ + 50 โ25x+5=10x+50 15 ๐ฅ = 45 โ ๐ฅ = < ๐ ๐ ๐ ๐ > 3 < / ๐ ๐ ๐ ๐ > 15x=45โx=3
Verification5x+1 = 16 > 0, x+5 = 8 > 0 valid. Substitute to check equality.
Final Answer3