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log2 la 5=a log2 la 3=b atunci log15 la 12?

Răspuns :

Folosesti formula: [tex] log_{a}(b) = \frac{ log_{x}(b)}{ log_{x}(a)} [/tex]

[tex]a= log_{15} (12) \\ b = log_{2}(3) \\ \\ log_{15}(12) = \frac{log_{2}(12)}{ log_{2}(15) } = \frac{log_{2}(4*3)}{ log_{2}(3*5) }=\\ = \frac{ log_{2}(4)+ log_{2}(3) }{ log_{2}(5) + log_{2}(3) } = \frac{2+b}{a+b} [/tex]