7. If real numbers $\mathrm { a } , \mathrm { b }$ satisfy $\frac { 1 } { a } + \frac { 2 } { b } = \sqrt { a b }$, then the minimum value of $ab$ is
A. $\sqrt { 2 }$
B. 2
C. $2 \sqrt { 2 }$
D. 4

$x , y$ are positive real numbers and
$$\frac { 2 y } { x + \frac { 1 } { y } } - \frac { 3 x } { y + \frac { 1 } { x } } = \frac { 5 x ^ { 2 } } { x \cdot y + 1 }$$
Given this, what is the ratio $\frac { x } { y }$?
A) $\frac { 2 } { 5 }$
B) $\frac { 1 } { 5 }$
C) $\frac { 3 } { 4 }$
D) $\frac { 1 } { 3 }$
E) $\frac { 1 } { 2 }$

Positive real numbers $a$ and $b$ satisfy the equality
$$a ^ { 2 } - 2 a b - 3 b ^ { 2 } = 0$$
Accordingly, what is the value of the expression $\frac { a + b } { a - b }$?
A) 2
B) 3
C) 4
D) 5
E) 6