1.
dx/x = ydy/(1+y)
ln(x) = y - ln(y) +c
2.
y = u(x)*v(x) = uv
y' = u'v + uv'
x(u'v + uv') + uv - e^x = 0
xu'v + xuv' +uv - e^x = 0
u'vx + u(xv' +v) = e^x
xv' + v = 0 (1) и u'vx = e^x (2)
ищем частное решение первого (1):
xv' = -v
dv/v = -dx/x
ln(v) = ln(1/х)
v = 1/x
подставляем во второе (2):
u' = e^x
u = e^x + С
Находим y:
y = uv = (e^x + С)/x
3.
x-y = -xy'
xy' = y-x
Замена y = t(x)x = tx
y' = t'x + t
t'x² + tx = tx - x
t'x = -1
t' = -1/x
t = - ln(x) + ln(C)
t = ln(C/x)
y = tx = x*ln(C/x)