# Thread: First Year Mathematics B (Integration, Series, Discrete Maths & Modelling)

1. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan Oh my bad I dropped a negative in that line which I later reintroduced. But wait

Factoring -v out I have

1 + 2/(1+v^2) = (1+v^2+2)/(1+v^2) = (3+v^2)/(1+v^2) right?

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Correct!  Reply With Quote

2. ## Re: MATH1231/1241/1251 SOS Thread But then.. Damn so I do have to p.f. it don't I haha

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3. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan  But then.. Damn so I do have to p.f. it don't I haha

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Yeah.  Reply With Quote

4. ## Re: MATH1231/1241/1251 SOS Thread

I've got a formula here for the normal vector to the surface:

<Fx(xo,yo), Fy(xo,yo), -1>

but then somewhere else I see them using this:

<-Fx(xo,yo), -Fy(xo,yo), 1>

Which one is correct?  Reply With Quote

5. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by Flop21 I've got a formula here for the normal vector to the surface:

<Fx(xo,yo), Fy(xo,yo), -1>

but then somewhere else I see them using this:

<-Fx(xo,yo), -Fy(xo,yo), 1>

Which one is correct?
We can use either for the normal, because those two vectors you've written are just negatives of each other, which means they are both valid normals (remember, two vectors that are just multiples of each other will both be valid direction vectors for a line).  Reply With Quote

6. ## Re: MATH1231/1241/1251 SOS Thread

I'm not sure what they want me to enter here. All results I get decimals, after finding the derivative of that integral.   Reply With Quote

7. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by Flop21 I'm not sure what they want me to enter here. All results I get decimals, after finding the derivative of that integral.   Reply With Quote

8. ## Re: MATH1231/1241/1251 SOS Thread

A bit lost in how to incorporate the nominal rate here. Need help with setting up the relevant ODE. I have a formula to find the effective rate for continuous compounding but it's taught in ACTL and not MATH.  Reply With Quote

9. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan A bit lost in how to incorporate the nominal rate here. Need help with setting up the relevant ODE. I have a formula to find the effective rate for continuous compounding but it's taught in ACTL and not MATH.  Reply With Quote

10. ## Re: MATH1231/1241/1251 SOS Thread

Lol they made us solve this differential equation by considering how it is an exact ODE. But the solution y=Ax just bugs me... is there a shorter way to doing this one haha  Reply With Quote

11. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan Lol they made us solve this differential equation by considering how it is an exact ODE. But the solution y=Ax just bugs me... is there a shorter way to doing this one haha

Note the LHS is d/dx (y/x).  Reply With Quote

12. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by InteGrand Note the LHS is d/dx (y/x).
Oops..........................

That moment when I saw it for this harder one but not the easier one  Reply With Quote

13. ## Re: MATH1231/1241/1251 SOS Thread

divide by e^x cos(y) a bit of rearrange you should get -cot(y)dy=dx  Reply With Quote

14. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan Oops..........................

That moment when I saw it for this harder one but not the easier one
Reverse product?  Reply With Quote

15. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by RenegadeMx divide by e^x cos(y) a bit of rearrange you should get -cot(y)dy=dx
I guess that works too.  Reply With Quote

16. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by Paradoxica Reverse product?
Yeah, I'm saying I missed reverse product for the first but saw it for the e^(xy) one Originally Posted by RenegadeMx divide by e^x cos(y) a bit of rearrange you should get -cot(y)dy=dx
Final answer ends up with exp(xy)cos(x)=C though  Reply With Quote

17. ## Re: MATH1231/1241/1251 SOS Thread

This is boring and tiring. What is the giveaway as to what values of p and q I am supposed to pick.  Reply With Quote

18. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan This is boring and tiring. What is the giveaway as to what values of p and q I am supposed to pick.

Remember that d/dz z^n = nz^(n-1), I think that should help you...

In this case, xy² ???  Reply With Quote

19. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by Paradoxica Remember that d/dz z^n = nz^(n-1), I think that should help you...
It's hard to juggle that when I have to consider two constants at a time and not just one  Reply With Quote

20. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan This is boring and tiring. What is the giveaway as to what values of p and q I am supposed to pick.  Reply With Quote

21. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan It's hard to juggle that when I have to consider two constants at a time and not just one
y is on the right, and there is a 3, so you want 3y². x is on the left and you have 4x² so you want 4x³. so xy² is a possibility...  Reply With Quote

22. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by InteGrand Andddd this is where intuition collides head on with mechanical rigour...  Reply With Quote

23. ## Re: MATH1231/1241/1251 SOS Thread

I can't identify the type of this one...

...unless I did my partial derivatives wrong  Reply With Quote

24. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by leehuan I can't identify the type of this one...

...unless I did my partial derivatives wrong
make dy/dx the subject and you'll see.

substitution y(x)=x.v(x)  Reply With Quote

25. ## Re: MATH1231/1241/1251 SOS Thread Originally Posted by laters make dy/dx the subject and you'll see.

substitution y(x)=x.v(x)
Oh crap I forgot about that g(y/x) because they said they'd give us the substitution in the exam  Reply With Quote

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