Thursday, 28 December 2017

solve differential equation for p; x²p³+yp²+p²x²y²+py³=0


p²(x²p+y) +y²p(px²+y)=0
(p²+y²p) (x²p+y)=0
p(p+y²) (x²p+y)=0

p=0
y-c=0

p+y²=0
dy/dx+y²=0
dy/y²=-dx
-1/y=-x+c
-1=-xy-cy
(cy-xy+1)

x²p+y=0
dy/dx+y/x²=0
integral factor=e^ʃ1/x²dx=e^-1/x
ye^-1/x=c

(y-c)(cy-xy+1)(ye^-1/x-c)=0


Wednesday, 27 December 2017

solve the differential equation for p ; xy(y-px)= x+yp



Xy²- pyx²-x-yp = 0
xy²-p(yx²+yp) –x= 0
xy²-x= p(yx²+y)
p= xy²-x/ yx²+y
dy/dx= x(y²-1)/ y(x²+1)
y/(y²-1) dy= x/ (x²+1)dx
 
let,
 y²-1= t
2ydy= dt
y dy= dt/2
and x²+1= v
2x dx= dv
x dx= dv/2

then,
dt/2t= dv/2v
1/2logt=1/2logv+logc
logt= logcv
t=  cv
(y²-1)= (x²+1)c
y²= (x²+1)c+1

Tuesday, 26 December 2017

solution of differential equation - (D^2 - 2D + 4)y = e^2x cos x.



The Auxiliary equation is,                                                                          
m² - 2m + 4 = 0
m = [2 ± √(4 – 16)] ∕ 2
m = 1 ± 2√3i/3
m = 1± √3i
complementary function = eˣ [A cos √3x + B sin√3x]
                                         = Aeˣ [cos √3x+B]
Particular integral=1/(D²-2D+4) e²ˣ cos x
                            = e²ˣ 1/[(D+2)²-2(D+2)+4] cos x
                            = e²ˣ 1/(D²+2D+4) cos x
                            = e²ˣ 1/(-1+2D+4) cos x
                            = e²ˣ 1/(2D+3)*(2D-3)/(2D-3) cos x
                            = e²ˣ 1/(4D²-9) 2 sin x- 3cos x
                            = -e²ˣ/13 [2 sin x- 3cos x]
y = complementary function + particular integral
y = eˣ [ A cos √3x + B sin √3x] - e²ˣ/13 [2 sin x – 3 cos x]