A suitable approximate solution for the boundary value problem du +2u +5u = 7 dr2 with appropriate boundary conditions is u(x) = x-6 + a*(x2+4*x+10) Find the residual of this approximate solution. Your answer should only consist of a single expression that represents the residual (not an equation) in terms of the variables a and x. Your answer should be expressed in terms of the variables a and x using the correct syntax. For example: 13*x-41+a*(3*x^2+55*x+81) residual =