You are Here: Home >< Maths

# 2nd order differential answer check watch

1. Find the general solution of the differential equation

a) Find the constants k an p such that

is a particular integral of the differential equation

and hence find the solution of this differential equation for which y= 0 and dy/dx = 3 at x = 0.

I've done all of this and I get the answer as:

and then I start substituting in and differentiating. My issue is that I get A = -3 and B = -2 whereas the book has them without the negative signs

(in fact the book has

as an answer, but I presumed that the e^3x at the end was a typo.

am I going horrendously wrong. Have I missed something, or is the book wrong?
2. I also presume the e^3x is a typo.

When x = 0, A + 3 = 0, right? So A = -3...
3. That's exactly what I'm getting. perhaps they factorise with -1 and forgot to put a minus outside the bracket.

So I'm right then and the book's wrong?

Score: Me 2 (so far): Book 1,536
4. Not a bad little total.
5. Can I get another answer check pls (and you're going to love this one!!!!)

I reckon I can get all the sine bits to cancel out using the addition rules, and then I'm left with the e bits.

I think I then get

i.e. it's e^-pi/3
6. (Original post by studienka)
Can I get another answer check pls (and you're going to love this one!!!!)

Hmm, let's see. I'm gonna call that expression P, purely a random letter choice because it was the first letter I saw on my whiteboard.

sin(a) = -sin(a+pi), so:

Might be wrong.
7. You're right,

for some reason I switch from Pi/2 to Pi/3 after my first line, so my workings are all correct, it just ends up as:

-e^-pi/2

I ignored the negative sign as the question involved moduli.

thnx for the check though.

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: August 17, 2007
Today on TSR

### University open days

Wed, 21 Nov '18
• Buckinghamshire New University
Wed, 21 Nov '18
• Heriot-Watt University
Wed, 21 Nov '18
Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams