a) Find the minimum positive integer $k$ so that for every positive integers $(x, y) $, for which $x/y^2$ and $y/x^2$, then $xy/(x+y) ^k$
b) Find the minimum positive integer $l$ so that for every positive integers $(x, y, z) $, for which $x/y^2$, $y/z^2$ and $z/x^2$, then $xyz/(x+y+z)^l$
### Part (a)
1. We need to find the minimum positive integer \( k \) such that for every pair of positive integers \( (x, y) \), if \( x \mid y^2 \) and \( y \mid x^2 \), then \( \frac{xy}{(x+y)^k} \) is an integer.
2. Given \( x \mid y^2 \) and \( y \mid x^2 \), we can write \( y = x^a \) and \( x = y^b \) for some integers \( a \) and \( b \).
3. Substituting \( y = x^a \) into \( x = y^b \), we get \( x = (x^a)^b = x^{ab} \). This implies \( ab = 1 \), so \( a = b = 1 \).
4. Therefore, \( x \mid y^2 \) and \( y \mid x^2 \) imply \( y = x \).
5. We need to find \( k \) such that \( \frac{xy}{(x+y)^k} \) is an integer. Since \( y = x \), we have \( \frac{x \cdot x}{(x + x)^k} = \frac{x^2}{(2x)^k} = \frac{x^2}{2^k x^k} = \frac{x^{2-k}}{2^k} \).
6. For \( \frac{x^{2-k}}{2^k} \) to be an integer, \( 2 - k \geq 0 \) and \( k \) must be an integer. Therefore, \( k \leq 2 \).
7. The minimum positive integer \( k \) is \( k = 2 \).

The final answer is \( \boxed{3} \).