The reals x and y satisfy log2x + logą(y2) = 5 and loggy + logą(x2) = 7 then the value of xy is
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Taking log on both sides of given equations.
log 3 log (3x) = log 4 log (4y);
log3(log 3+log x)=log4(log 4+logy)
[ log(ab)=log a+log b] Rightarrow
(i) And, log x log 4 = log y log 3; log x(log 4)=(log y)log 3 Rightarrow
(ii) From
(i) (log 4)^ 2 -(log 3)^ 2 =log 3 log x-log4 logy Rightarrow(mi) From
(ii) log x log 3 = log y log 4 = lambda(say) Rightarrow
(iv) From (iv) and
(iii) (log 4) ^ 2 - (log 3) ^ 2 = [(log 3) ^ 2 - (log 4) ^ 2] lambda;
lambda =
- 1; log x =
- log 3 = log 1/3; Rightarrow logy=
-log 4=log 1 4;
therefore x= 1 3 ,y= 1 4
Hence, Verification complete
Note :-
Remember it's easy just we have to subtract it.
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