1. Find the general solution of (general integral) of the differential equation.
1.9 (sin (x + y) + sin (x - y)) dx + dy / cosy = 0

2. Find the general solution of (general integral) of the differential equation.
2.9 y + 2y - y2 = 0

3. Find the general solution of (general integral) of the differential equation.
3.9 xy - y = (x + y) ln ((x + y) / x)

4. Find a particular solution of (partial integral) of the differential equation.
4.9 x2y + xy + 1 = 0, y (1) = 0.

5. Find the general solution of the differential equation.
5.9 2y- x / y = xy / (x2-1)

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