Equations from given list are of standard kinds. For every question, determine as many classes as you can such that equation belongs to class or could be converted, by elementary algebraic transformations, into equation belonging. Verify the findings.
i) y^{2} +(X^{2}-4xy)y{ }'= 0
ii) y{}'+1 = \frac{1}{x+y}
iii) y{}'= \frac{y}{x}+\frac{1}{x}
iv) y{}'+1 = -\frac{x}{x+y}