Recent content by jakobs

Sorry, I posted wrong, don't know what happened. but pi*(-(1/2))=-1,57 pi*(-(1/1))=-3,14 -1,57-(-3,14)= 1,57 is this the right answer?

Homework Statement y=(1/x) is rotating around the x-axis. find the volume for the figure between x=1 and x=2 Homework Equations The Attempt at a Solution V=pi y2 = pi*(1/x)2 V= 1∫2 pi(1/x)2dx which gives V= 1∫2 pi(1/x2)dx A primitive function for (1/x2) is -(1/x) V=1∫2...

Everything adds up, it must be correct! What a great feeling I get from seeing that it is right :)

i see it now, I thought in the wrong way, I can't take the 2 away from C. Can I do it like this? 2*1 + 0 = 2*(C+D) - 2C - 4D ⇔ 2 = 2C - 2C + 2D - 4D ⇔ -2D = 2 ⇔ D = -1 This gives 1 = C - 1 ⇔ C = 2

I think it gets wrong after what I highlighted. Is there someone who can explain a little bit, so I can get in the right direction of solving this one?

I don't want to come across as stupid, but how do I do that?

Homework Statement This is my first big differential equation that I have solved by myself, and I wanted to see if it is correct done, or what I have done wrong with it. Would really appreciate if somebody could take a look on it. y''+6y'+8y=0 when y(0)=1 and y'(0)=0 The Attempt at a Solution...

Okay, so the answer to the problem is: y=x*e-0,4x y'=(1-0,4x)*e-0,4x y'=(1-0,4x=0 x=2.5 e-0,4x is always >0 And this classifies as the correct answer?

According to some earlier posts the solution to 1-0.4x =0 solves Y'=0 If x is 2.5 then it will be 0. But what should I do with e-0,4x?

I don't understand the whole thing :confused: Can somebody show all steps to solving this one? I really need to learn it.

So I only have to solve 1-0,4x=0 and that will be the whole answer for the whole equation?

I'm not completely understand everything you wrote there, and I feel a bit stupid now.

So, the answer should be f(x)=1/2 sin(x) ?

Homework Statement I have y'(x)= xcos(x2) How do I get the primitive function for this? Homework Equations The Attempt at a Solution I know that f'(x)=2xcos(x2) is f(x)=sin(x2) How will removing that 2 in front of xcos affect the primitive function?

Homework Statement I'm going to solve the equation Y'=0 if Y=x*e-0,4xHomework Equations The Attempt at a Solution I can come as far as to Y'=(1-0,4x)*e-0,4x Where do I go from here? Can i just write (1-0,4x)*e-0,4x=0 ? I can solve the easier kinds of these equations, but this one is the...