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Question

Let $f(x, y)$ be a continuously differentiable homogenous function of degree 4. Which of the following is necessarily true?

The correct answer is
$x \frac{\partial f(x, y)}{\partial x} + y \frac{\partial f(x, y)}{\partial y} = 4f(x, y)$

Homogeneous Function Degree 4 Solution

This problem involves Euler's Homogeneous Function Theorem, which relates a homogeneous function to its partial derivatives.

Euler's Theorem Statement

If $f(x, y)$ is a continuously differentiable homogeneous function of degree $n$, then it satisfies the following identity:

$x \frac{\partial f(x, y)}{\partial x} + y \frac{\partial f(x, y)}{\partial y} = n f(x, y)$

Applying to the Problem

The question states that $f(x, y)$ is a homogeneous function of degree 4. Thus, we have $n = 4$. Substituting $n=4$ into Euler's theorem gives:

$x \frac{\partial f(x, y)}{\partial x} + y \frac{\partial f(x, y)}{\partial y} = 4f(x, y)$

Result

This identity must necessarily be true for the given function. Comparing this result with the options provided, it matches Option 3.

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Important Questions from Algebra

  1. 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
  2. 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) ___.

  3. 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).
  4. 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 $xyz$?
  5. Two points $(4, p)$ and $(0, q)$ lie on a straight line having a slope of $3/4$. The value of $(p – q)$ is
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