0 years, 95 days

## Can't solve a differential equation...

Maple 2019

I have an ordinary differential equation to be solved. when I give numeric values to B,H and L__1 (for example B=10,H=10,L__1=4), everything works fine and equations eq37a will be solved.

but when B,H and L__1 are symbolic parameters, dsolve give me this error " Error, (in dsolve) give the main variable as a second argument". and I don't know what it means.

is there any way to solve the ODE with symbolic B,H and L__1??

 > restart; #B:=10; #H:=10; #L__1:=4; eq0:=R__i=(1/2)*B+L__1; eq01:=R__f=C+(1/2)*B+L__1; eq02:=theta__1=arctan((H/2)/(B/2 + L__1)); eq03:=theta__2=Pi - arctan((H/2)/(B/2 - L__1)); eq43:= v__beta(r,theta,beta)= v__m(beta)*(1-(r^2/((R__max(theta,beta))^2))); eq39:=R(beta)=R__i+2*beta*(R__f-R__i)/Pi; eq39a:=simplify(subs([eq0,eq01], eq39)); eq38:=R__max(theta,beta)=R__max(theta,0)*(R(beta)/R__i); eq41:=R__max(theta,0)=piecewise(theta<=rhs(eq02),(B/2+L__1)/cos(theta),theta<=rhs(eq03),(H/2)/sin(theta),rhs(eq03)= 2 , H > 0 , B > 0 , L__1 > 0; eq44b:= v__m(beta)= rhs(eq44a) * B * H; eq47:=subs([eq44b,eq38a],eq43);
 (1)
 > eq37:=diff(v__r(r, theta, beta),r)*r*(R__f-r*cos(theta))+v__r(r,theta,beta)*(R__f-2*r*cos(theta))+r*diff(v__beta(r,theta,beta),beta)=0; eq37a:=simplify(expand(subs(eq47, eq37)));
 (2)
 > bc:=v__r(rhs(eq38a),theta,beta)=0;
 (3)
 > sol3:=simplify(dsolve([eq37a,bc], v__r(r, theta,beta)));
 >

## Can't solve an integral...

Maple 2019

Maple can't solve the following symbolic integration for me and it remains in the state of evaluating when I use simplify and nothing happens after hours.. any solution?

I was thinking maybe there is something wrong with my maple !!?

 > eq0:=R__i=(1/2)*d+L__1; eq00:=R__f=c+(1/2)*d+L__1; eq39:=R(beta)=R__i+2*beta*(R__f-R__i)/Pi; eq39a:=simplify(subs([eq0,eq00], eq39)); eq38:=R__max(theta,beta)=R__max(theta,0)*(R(beta)/R__i); eq41:=R__max(theta,0)=((2*L__1*cos(theta)) + sqrt(d^2 - 2*(L__1)^2 + 2*(L__1)^2*cos(2*theta)))/2; eq38a:= simplify(subs([eq41,eq39a,eq0], eq38));
 (1)
 > eq44 := v__m(beta) = 1/int((1 - r^2/R__max(theta, beta)^2)*r, [r = 0 .. R__max(theta, beta), theta = 0 .. 2*Pi]);
 (2)
 > eq44a:=simplify(subs(eq38a,eq44));
 >

## Problem in Solving a first-order linear ...

Maple 2017

Hello,

I have a problem in solving a differential equation in maple. I got an error which is "unexpected occurence of the variables..." .  I have uploaded my full problem as a pdf and maple worksheet (mw) files.

Untitled_(4).pdf

Prob.mw

## Problem in Solving integral in Maple...

Maple 2017

Hello,

I have a problem in solving an integral in maple. I can't solve the below integral in maple and it returns the integral itself to me. I also attach an image from the integral if here is not clearly shown. I want maple to return me just a number. can anyone help me in this?

Thank you

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