Q 31 :

Let the solution curve of the differential equation x dy-y dx=x2+y2 dx,  x>0, y(1)=0 be y=y(x). Then y(3) is equal to          [2026]

  • 1

     

  • 2

     

  • 6

     

  • 4

     

(4)

x dy-y dxx2=x2+y2x2dx

d(yx)=1+y2x2·1xdx

∫d(yx)1+(yx)2=∫1xdx

=ln(yx+1+y2x2)=lnx+lnk=lnkx

⇒y+x2+y2=kx2

0+1=k

⇒y+x2+y2=x2

y+9+y2=9

y=4



Q 32 :

Let y=y(x) be the solution of the differential equation secxdydx-2y=2+3sinx,  x∈(-π2,π2), y(0)=-74.Then y(π6) is equal to:    [2026]

  • -52

     

  • -54

     

  • -33-7

     

  • -32-7

     

(1)

dydx-2ycosx=2cosx+3sinxcosx

I.F.=e-2sinx

e-2sinx y=∫e-2sinx(3sinxcosx+2cosx)dx

y.e-2sinx=e-2sinx(-32sinx-74)+C

⇒y=-32sinx-74+Ce2sinx

∵ y(0)=-74⇒C=0

y(π6)=-32·12-74=-52



Q 33 :

Let f(x)=x3+x2f'(1)+2xf''(2)+f'''(3),  x∈R. Then the value of f'(5) is             [2026]

  • 1175

     

  • 25

     

  • 625

     

  • 6575

     

(1)

f'(x)=3x2+2xf'(1)+2f''(2)

f''(x)=6x+2f'(1)

f''(2)=12+2f'(1)

∴ f'(x)=3x2+2xf'(1)+2(12+2f'(1))

f'(x)=3x2+2(x+2)f'(1)+24

Putting x=1

f'(1)=3+6f'(1)+24

-5f'(1)=27⇒f'(1)=-275

∴ f''(2)=12+2(-275)=12-545=65

∴ f'(x)=3x2-545x+125

∴ f'(5)=75-54+125=1175



Q 34 :

If y=y(x) satisfies the differential equation 16(x+9x)(4+9+x)cosy dy=(1+2siny) dx,  x>0 and y(256)=π2, y(49)=α, then 2 sinα is equal to_____.   [2026]

  • 3(2-1)

     

  • 2-1

     

  • 2(2-1)

     

  • 22-1

     

(4)

∫cosy1+2siny dy=∫dx16(9x+x)(4+9+x)

                                          4+9+x=t

                                        129+x×dx2x=1 dx

12ln|1+2siny|=∫4 dt16t+C

12ln|1+2siny|=14ln|4+9+x|+C

12ln(2siny+1)=14ln|4+9+x|+C

Substituting (256,π2)

12ln3=12ln3+C               C=0

Substituting (49,α)

12ln(2sinα+1)=14ln8

ln(2sinα+1)=12ln8

ln(2sinα+1)=ln(22)

2sinα+1=22

2sinα=22-1



Q 35 :

Let y = y(x) be the solution of the differential equation xdydx-sin2y=x3(2-x3)cos2y,  x≠0. If y(2) = 0, then tan(y(1)) is equal to        [2026]

  • 34

     

  • -34

     

  • 74

     

  • -74

     

(3)

xdydx-sin2y=x3(2-x3)cos2y

sec2ydydx-2tany·1x=x2(2-x3)

tany=t⇒sec2ydydx=dtdx

dtdx-2tx=x2(2-x3)  (LDE)

I.F.=e∫-2xdx=e-2lnx=1x2

∴ tx2=∫1x2x2(2-x3)dx+C

tanyx2=2x-x44+C

y(2)=0⇒0=4-4+C⇒C=0

tany=2x3-14x6

x=1⇒tany=2-14=74



Q 36 :

The solution of the differential equation  (1-xy-x5y5)dx-x2(x4y4+1)dy=0 given by (c is arbitrary constant)

  • x=ce xy+15x5y5

     

  • x=ce xy-15x5y5

     

  • x=ce x2y2+15x5y5

     

  • x=ce x2y2-15x5y5

     

(1)

The given equation is dx-x(ydx+xdy)=x5y4(ydx+xdy)

⇒dxx=(1+x4y4)d(xy)⇒lnx=xy+15x5y5+lnc

⇒x=ce xy+15x5y5



Q 37 :

Let y=f(x) satisfy the differential equation dydx=2xe-y, ∀x∈R. If y'(1)=1 then the number of solutions of the equation f(x)=f'(x) in (0,∞) is

  • 1

     

  • 2

     

  • 3

     

  • zero

     

(1)

∫ey dy=∫2x dx⇒f(x)=ln(x2+c)

f'(1)=1⇒C=1



Q 38 :

Let y=y(x) be the solution of the differential equation dydx+2y=f(x), where f(x)={1,x∈[0,1]0,otherwise.  If y(0)=0, then y(ln2) is

  • e2-14e2

     

  • e2-12e2

     

  • 14

     

  • 38

     

(4)

When x∈[0,1], then dydx+2y=1⇒y=12+C1e-2x  

∵  y(0)=0⇒y(x)=12-12e-2x

Here, y(1)=12-12e-2x=e2-12e2

When x∉[0,1] then dydx+2y=0⇒C2=e2-12

∵  y(1)=e2-12⇒e2-12=C2e-2⇒C2=e2-12

∵  y(x)=(e2-12)e-2x⇒y(32)=e2-12e3



Q 39 :

The Solution of the differential equation (1+x3)dydx+3x2y+cos2x-1=0

  • y(1+x3)=x2-14sin2x+C

     

  • y(1+x3)=x2+14sin2x+C

     

  • y(1+x3)=x4-12sin2x+C

     

  • y(1-x3)=x2-14sin2x+C

     

(1)

I.F=e∫(3x21+x3)dx=1+x3

y(1+x3)=∫1-cos(2x)2dx

y(1+x3)=x2-14sin2x+C



Q 40 :

Let y=y(x), y>0 be a solution curve of the differential equation (1+x2) dy=y(x-y) dx. If y(0)=1 and y(22)=β, then

  • e3β-1=e(3+22)

     

  • eβ-1=e-2(5+2)

     

  • eβ-1=e-2(3+22)

     

  • e3β-1=e(5+2)

     

(1)

Given, (1+x2) dy=y(x-y) dx

Where, y(0)=1,  y(22)=β

dy=(yx-y21+x2)dx

dydx+y(-x1+x2)=(-11+x2)y2

Divide by y2 both sides and proceed.



Q 41 :

Let the solution curve y=f(x) of the differential equation dydx+xyx2-1=15x4+4x3+4x+11-x2,  x∈(-1,1) passes through the origin. Then ∫-1/21/2f(x) dxx2+2 is equal to.

  • π6

     

  • π6-34

     

  • π3-34

     

  • π3-14

     

(2)

I.F.=e∫x dxx2-1=1-x2

y=f(x)=3x5+x4+2x2+x1-x2

=∫-1/21/2f(x)(x2+2) dx=π6-14



Q 42 :

The function y=f(x) is the solution of the differential equation dydx+xyx2-1=x4+21-x2 in (-1,1) satisfying f(0)=0. Then 2∫-3/23/2f(x) dx is

  • 2π3+32

     

  • 2π3-32

     

  • π6-34

     

  • π6-32

     

(2)

dydx+xx2-1y=x4+2x1-x2

The I.F. of this differential equation is     e∫xx2-1 dx=e-∫x1-x2 dx=e12log(1-x2)=1-x2

The solution is given by   y1-x2=∫x3+21-x21-x2 dx+λ

=∫(x4+2x) dx+λ=x55+x2+λ

At y(0)=0⇒λ=0⇒y1-x2=x55+x2

∫-3/23/2x55+x21-x2 dx=∫-3/23/2x21-x2 dx

(The other part is odd) =2∫03/2x21-x2 dx

Let x=sinθ, we get

I=2∫0π/3sin2θcosθcosθ dθ

  =2∫0π/3sin2θ dθ

   =∫0π/3(1-cos2θ) dθ

    =[θ-sin2θ2]0π/3

     =π3-34

∴  2I=2π3-32



Q 43 :

If dydx=2x+y-2x2y, y(0)=1, then y(1)=

  • log2(2+e)

     

  • log2(1+e)

     

  • log2(2e3)

     

  • log2(1+e2)

     

(2)

dydx=2x+y-2x2y⇒dydx=2x(2y-1)2y⇒2y2y-1dy=2xdx⇒∫2y2y-1dy=∫2xdx

⇒log(2y-1)log2=2xlog2+c, y(0)=1⇒0=1log2+c⇒c=-1log2

∴ log(2y-1)log2=2xlog2-1log2⇒log(2y-1)=2x-1

If x=1 than log(2y-1)=2-1=1⇒2y-1=e⇒2y=e+1⇒y=log2(e+1)

⇒y(1)=log2(e+1)



Q 44 :

In column I differential equations are given in column II their solutions are given then match them

  Column I   Column II
A) ydydx+x=0 p) 2y=x2+c
B) xdydx+y=0 q) x2+y2=c
C) dydx=x r) xy=c
D) dxdy=y s) y2=2x+c

 

  • A – r, B – q, C – p, D – s

     

  • A – q, B – r, C – p, D – s

     

  • A – s, B – q, C – p, D – r

     

  • A – p, B – q, C – r, D – s

     

(2)

Use variable seperable