Thread: Can someone check my answers?

Hey people,

I would just like a few of my answers to be checked, if anyone wants to,

1) y'=e(-y)-1

I got ln(1-e(y))+x=c, but i think this is wrong(it doesn't match the given answer)

My working was:

dy/dx=1/e(y)-1
dy/dx=(1-e(y))/e(y)
int (1-e(y))/e(y) dy -int 1 dx=0
ln(1-e(y))+x=c

2) (dy/dx)tanx+tany=0

I got sinysinx=c

3) Find the general solution of:

d2y/dx2-5dy/dx+4y=2e(3x)

I got: Ae(4x)+Be(x)-e(3x)

4) d2y/dt2+4y=12cos(2t)

i) find Yc:

I got Yc=Acos(2t)+Bsin(2t)

ii) find the full general solution:

I got y=Acos(2t)+Bsin(2t)+3tsin(2t)

iii) given y'(0)=0 and y(0)=0 find the full solution

I got y=3tsin(2t)

5) evaluate int e(2x)sinx dx via trap rule, simpsons 1/3rd and gauss integration. With 4 strips for trapezoidal/simpsons.

I got:

Trap: 23.02829

Simp: 22.70988612

Gauss: 22.768

Any answer checks would be greatly appreciated, especially for the first question.

Originally Posted by deragon999

Hey people,

I would just like a few of my answers to be checked, if anyone wants to,

1) y'=e(-y)-1

I got ln(1-e(y))+x=c, but i think this is wrong(it doesn't match the given answer)

My working was:

dy/dx=1/e(y)-1
dy/dx=(1-e(y))/e(y)
int (1-e(y))/e(y) dy -int 1 dx=0
ln(1-e(y))+x=c

2) (dy/dx)tanx+tany=0

I got sinysinx=c

3) Find the general solution of:

d2y/dx2-5dy/dx+4y=2e(3x)

I got: Ae(4x)+Be(x)-e(3x)

4) d2y/dt2+4y=12cos(2t)

i) find Yc:

I got Yc=Acos(2t)+Bsin(2t)

ii) find the full general solution:

I got y=Acos(2t)+Bsin(2t)+3tsin(2t)

iii) given y'(0)=0 and y(0)=0 find the full solution

I got y=3tsin(2t)

5) evaluate int e(2x)sinx dx via trap rule, simpsons 1/3rd and gauss integration. With 4 strips for trapezoidal/simpsons.

I got:

Trap: 23.02829

Simp: 22.70988612

Gauss: 22.768

Any answer checks would be greatly appreciated, especially for the first question.

Dear deragon999,

I suppose you mean in the first question. Is'nt??

If that is so,













; Where C is an arbitary constant.

Hope this will help you.

Sudharaka

Thanks, can you show me how you got



Thanks,
Simon

Originally Posted by deragon999

Sudharaka

Thanks, can you show me how you got



Thanks,
Simon

Dear deragon999,



Was it helpful?

Haha not relly, that bit i had already done in my working, the bit that you did different to me was taking -1 out of the dy integral

Thanks you for all your time spent anyway