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Question

For positive non-zero real variables $x$ and $y$, if
$ln\left(\frac{x+y}{2}\right) = \frac{1}{2} [ln\left(x\right) + ln\left(y\right)]$
then, the value of $\frac{x}{y} + \frac{y}{x}$ is

The correct answer is
2

Logarithmic Equation Simplification

We are given the equation for positive non-zero real variables $x$ and $y$: $ ln\left(\frac{x+y}{2}\right) = \frac{1}{2} [ln\left(x\right) + ln\left(y\right)] $

Applying Logarithm Properties

Using the logarithm property $ln(a) + ln(b) = ln(ab)$, the right side becomes:

$ \frac{1}{2} [ln\left(x\right) + ln\left(y\right)] = \frac{1}{2} ln(xy) $

Using the property $c \cdot ln(a) = ln(a^c)$, this simplifies to:

$ ln((xy)^{\frac{1}{2}}) = ln(\sqrt{xy}) $

Equating Arguments

The equation now is: $ ln\left(\frac{x+y}{2}\right) = ln(\sqrt{xy}) $ Since the natural logarithm function is one-to-one, we can equate the arguments:

$ \frac{x+y}{2} = \sqrt{xy} $

Solving for Variable Relationship

Multiply both sides by 2:

$ x+y = 2\sqrt{xy} $

Square both sides to eliminate the square root:

$ (x+y)^2 = (2\sqrt{xy})^2 $ $ x^2 + 2xy + y^2 = 4xy $

Rearrange the terms to form a quadratic expression:

$ x^2 - 2xy + y^2 = 0 $

Factor the expression, which is a perfect square:

$ (x-y)^2 = 0 $

Taking the square root gives:

$ x-y = 0 $ $ x = y $

Calculating the Required Value

We need to find the value of $\frac{x}{y} + \frac{y}{x}$. Since we found $x=y$, we can substitute $y$ with $x$ (or vice versa):

$ \frac{x}{x} + \frac{x}{x} = 1 + 1 $ $ = 2 $

Therefore, the value of $\frac{x}{y} + \frac{y}{x}$ is 2.

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Important Questions from Algebra

  1. Given $f(x, y) = x^2 - 2xy + y^2$ 

    The complete contour of the equation $f(x, y) = 1$ is described by the option(s) ___.

  2. It is given that $x$ and $y$ are integers in the following equation:
    $$(x + y - 7)^2 + (y + 3x - 13)^2 = 0$$
    The value of $(x^3 + y^3)$ is ________ (in integer).
  3. If $pqr \neq 0$ and $p^{-x} = \frac{1}{q}$, $q^{-y} = \frac{1}{r}$, $r^{-z} = \frac{1}{p}$, what is the value of the product $xyz$?
  4. Two points $(4, p)$ and $(0, q)$ lie on a straight line having a slope of $3/4$. The value of $(p – q)$ is
  5. If $Pe^x = Qe^{-x}$ for all real values of $x$, which one of the following statements is true?
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