To find the derivatives dy/dx or
y':
1)xy+x+y = 5-x.Here find the derivatives term by term
and then group the terms with y' and solve for y'.
(xy)'
+x' +y' = (5-x)'.
x'y+xy' +1 + y' = (5)'-
x'.
y+xy' +1+ y' = 0-1.
xy' +
y' = -y-2.
(x+1)y' =
-(y+2).
y' =
(y+2)/(x+1).
2)ctg^3y +2x-3y =
8.
Differentiate with respect to
x:
(ctg^3y)' = {ctgy)^3} = 3ctg^2y*(ctgy)' =
3ctg^2y*(-cosec^2y)*y'=-3y'cos^2y.
(2x)' =
2.
(-3y)' = -3y'.
(8)' =
0.
Therefore (ctg^3y +2x-3y)' =
(8)'.
-3y'cosy +2-3y' = 0.
Now
we group the terms with y' together and solve for
y':
-3y'cosy -3y' =
-2.
-3y'(3+cosy) = -2.
y' =
2/(3+cosy).
3)xy =
(1-x-y)^2.
Differentiate both
sides.
(xy)' = {(1-x-y)^2
}'.
xy'+y =
2(1-x-y)^(2-1)*(1-x-y)'.
xy'+y =
2(1-x-y)(-1-y').
xy' +y = -2+2x+2y -
2y'(1-x-y).
xy'+2y'(1-x-y) =
-2+2x+2y-y.
y'(2-x-2y) =
-2+2x+y.
y' = (-2+2x+y)/(2-x-2y).
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