Questions
If and 1 are in A.P, then x is equal to
detailed solution
Correct option is B
From the given condition, we must have 2log4(21−x+1)=log2(5.2x+1)+1⇒ 2log4(21−x+1)log4=log2(5.2x+1)log2+1⇒ 2log(21−x+1)log4=log(5.2x+1)log2+1⇒ log(21−x+1)=log[(5.2x+1)2]⇒ 21−x+1=5.2x.2+2Now, put 2x=y, so that2y+1=10y+2⇒ 10y2+y−2=0⇒ (5y−2)(2y+1)=0Which meansy=2/5 or y=−1/2. Since y=2xcannot be negative, we havey=2x=2/5=0.4 ie., x=log2(0.4). But 2x=2/5can also express in the formx=log(2/5)log2=1−log5log2.Similar Questions
If the first, second and the last terms of an A.P. are respectively, then the sum of the is
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