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Question

(i) If log (a+1)=log (4a3)log 3; find a.

(ii) If 2 log ylog x3=0, express x in terms of y.

(iii) Prove that : log10 125=3(1log10 2).

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Solution

(i)

g i v e n space t h a t log open parentheses a plus 1 close parentheses equals log open parentheses 4 a minus 3 close parentheses minus log 3 rightwards double arrow log open parentheses a plus 1 close parentheses equals log open parentheses fraction numerator 4 a minus 3 over denominator 3 end fraction close parentheses rightwards double arrow a plus 1 equals fraction numerator 4 a minus 3 over denominator 3 end fraction rightwards double arrow 3 a plus 3 equals 4 a minus 3 rightwards double arrow a equals 6

(ii)

2 log y minus log x minus 3 equals 0 rightwards double arrow 2 log y minus log x equals 3 rightwards double arrow log y squared minus log x equals log 1000 rightwards double arrow l o g open parentheses y squared over x close parentheses equals log 1000 rightwards double arrow x equals y squared over 1000

(iii)

log subscript 10 125 equals 3 open parentheses 1 minus log subscript 10 2 close parentheses L H S equals log subscript 10 125 rightwards double arrow log subscript 10 5 cubed rightwards double arrow 3 log subscript 10 5 minus negative negative negative open parentheses 1 close parentheses R H S equals 3 open parentheses 1 minus log subscript 10 2 close parentheses rightwards double arrow 3 open parentheses log subscript 10 10 minus log subscript 10 2 close parentheses rightwards double arrow 3 log subscript 10 open parentheses 10 over 2 close parentheses rightwards double arrow 3 log subscript 2 5 minus negative negative open parentheses 2 close parentheses f r o m e open parentheses 1 close parentheses space a n d space open parentheses 2 close parentheses comma w e space h a v e space L H S equals R H S h e n c e space p r o v e d


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