Cho $\Large \log_{3}5 = a$, khi đó $\Large \log_{3}\dfrac{3}{25}$ bằng

Cho $\Large \log_{3}5 = a$, khi đó $\Large \log_{3}\dfrac{3}{25}$ bằng

• A.

  $\Large 1 - 2a$

• B.

  $\Large \dfrac{1}{2a}$

• C.

  $\Large 1 - \dfrac{a}{2}$

• D.

  $\Large 1 + \dfrac{a}{2}$

Chọn A

Ta có:

$\Large \log_{3}\dfrac{3}{25}= \log_{3}3 -  \log_{3}25= \log_{3}3 -  \log_{3}5^{2} = \log_{3}3 -  2\log_{3}5 = 1 - 2a$