then, $\frac{p^2}{q^2} + \frac{q^2}{p^2} = $
We are given that $p$ and $q$ are positive integers and the equation:
$ \frac{p}{q} + \frac{q}{p} = 3 $
We need to find the value of:
$ \frac{p^2}{q^2} + \frac{q^2}{p^2} $
Let $x = \frac{p}{q}$. The given equation can be rewritten in terms of $x$ as:
$ x + \frac{1}{x} = 3 $
The expression we need to find is $\frac{p^2}{q^2} + \frac{q^2}{p^2}$, which is equivalent to $x^2 + \frac{1}{x^2}$.
Consider the square of the term $(x + \frac{1}{x})$:
$ \left(x + \frac{1}{x}\right)^2 = x^2 + 2(x)\left(\frac{1}{x}\right) + \left(\frac{1}{x}\right)^2 $
$ \left(x + \frac{1}{x}\right)^2 = x^2 + 2 + \frac{1}{x^2} $
Rearrange the formula to solve for $x^2 + \frac{1}{x^2}$:
$ x^2 + \frac{1}{x^2} = \left(x + \frac{1}{x}\right)^2 - 2 $
Substitute the given value $\left(x + \frac{1}{x} = 3\right)$ into the rearranged formula:
$ x^2 + \frac{1}{x^2} = (3)^2 - 2 $
$ x^2 + \frac{1}{x^2} = 9 - 2 $
$ x^2 + \frac{1}{x^2} = 7 $
Since $x = \frac{p}{q}$, we have $x^2 = \frac{p^2}{q^2}$ and $\frac{1}{x^2} = \frac{q^2}{p^2}$. Therefore:
$ \frac{p^2}{q^2} + \frac{q^2}{p^2} = 7 $
The value of $\frac{p^2}{q^2} + \frac{q^2}{p^2}$ is 7.
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) ___.