Basic Differential Equation Can you check my work?

[Jac8897]

Homework Statement

state the order and linearity of the diff eq

(d^2u/dr^2)+(du/dr)+(u)=cos(r+u)

1)the order is the second order. since the highest derivative is 2
2) the term cos(r+u) is not linear therefore this equation is not linear.

is my reasoning for 2) right since the dependent variable is contain in cos(r+u) that makes this non-linear, right?

 

[hunt_mat]

Looks good to me.