[[_3rd_order, _missing_y]]
Book solution method
TO DO
Mathematica ✓
cpu = 0.680945 (sec), leaf count = 56
Maple ✓
cpu = 28.87 (sec), leaf count = 276
DSolve[-y'[x] + (2*Cot[x] + Csc[x])*y''[x] + y'''[x] == Cot[x],y[x],x]
Mathematica raw output
{{y[x] -> -((x*C[2])/Sqrt[2]) + C[3] + ArcSin[Cos[x]]*Cot[x/2] - (Cot[x/2]*(2*C[
1] + C[2]*Log[2*(1 + Cos[x])]))/Sqrt[2]}}
Maple raw input
dsolve(diff(diff(diff(y(x),x),x),x)+(2*cot(x)+csc(x))*diff(diff(y(x),x),x)-diff(y(x),x) = cot(x), y(x),'implicit')
Maple raw output
y(x) = (-_C1*Pi*csgn(I*exp(-I*x)*(exp(I*x)+1)^2)^3+_C1*Pi*(csgn(I*exp(-I*x))+csg
n(I*(exp(I*x)+1)^2))*csgn(I*exp(-I*x)*(exp(I*x)+1)^2)^2-_C1*Pi*csgn(I*(exp(I*x)+
1)^2)*csgn(I*exp(-I*x))*csgn(I*exp(-I*x)*(exp(I*x)+1)^2)-_C1*Pi*csgn(I*(exp(I*x)
+1)^2)^3+2*_C1*Pi*csgn(I+I*exp(I*x))*csgn(I*(exp(I*x)+1)^2)^2-_C1*Pi*csgn(I+I*ex
p(I*x))^2*csgn(I*(exp(I*x)+1)^2)-2*I*_C1*(exp(I*x)+1)*ln(exp(I*x)+1)+2*I*_C1*ln(
exp(I*x))+(-I*x-2*_C1*x+_C3)*exp(I*x)+2*I*ln(2)*_C1-I*x-2*I*_C2+2*_C1*x-_C3)/(ex
p(I*x)-1)