MCQ
The solution of the equation ${\log _7}{\log _5}$ $(\sqrt {{x^2} + 5 + x} ) = 0$
  • A
    $x = 2$
  • B
    $x = 3$
  • $x = 4$
  • D
    $x = - 2$

Answer

Correct option: C.
$x = 4$
c
(c) ${\log _7}{\log _5}(\sqrt {{x^2} + 5 + x} ) = 0 = {\log _7}1$

$ \Rightarrow $ ${({x^2} + 5 + x)^{1/2}} = 5$

$ \Rightarrow $ $({x^2} + x + 5) = 25$$ \Rightarrow $ ${x^2} + x - 20 = 0$

$ \Rightarrow $ $ (x - 4)\,(x + 5) = 0$ $ \Rightarrow $ $ x = \,4,\, - 5$ ==> $x = 4$.

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