课程名称︰常微分方程导论 课程性质︰数学系大二必修 课程教师︰林绍雄 开课学院：数学系 开课系所︰数学系 考试日期（年月日）︰104年01月10日 考试时限（分钟）：180分钟 试题 : The following problems has a total of 140 points. Please write down your computational steps, or proof reasoning clearly on the answer sheets. A.Apply the method of the Laplace transforms to solve the following problems. Each has 11 points. (a)Solve the system x"+x-y=0, y"+y-x=tδ(t-2), x(0)=y(0)=0, x'(0)=-2, y'(0)=1 (b)Find L{J1(t)}, where J1(t) is the Bessel function of order 1 (c)Solve y'+y-∫y(η)sin(t-η)dη(from 0 to t)=-cost, y(0)=1 B.(20 points) Solve xy"+y'+y=0 by the power series method in x>0. What are the region of convergence for the solutions? C.(16 points) Solve the Riccati equation IVP problem y'=y^2+x^3, y(0)=0 D.(18 points) Find the equilibria of the plane system x'=y-x^2+2, y'=x^2-xy. Draw the phase portrait of the linearized plane system at each equilibrium, and determine its type. E.(20 points) Draw the phase portrait of the prey-predator system x'=x(2-ax-y) , y'=y(-1+ax) (where a>0 is a constant) in x≧0, y≧0. Discuss the type of each equilibria first, then apply the Poincare-Bendixon theorem to finish the draw. What is ω((α,β)) for all α≧0, β≧0 ? F.Let f: R → R be a C1 function. The phase coordinate (x,y) for the equation x"+f(x)=0 is given by y=x' (a)(9 points) Prove that every equilibria are of the form (x*,0) with f(x*)=0, and when f'(x*)≠0, this equilibrium is either a center or a saddle. (b)(8 points) Prove that this system has no limit cycles. G.Determine which of the following statements is true. Prove your answer. Each has 8 points. (a)x=0 is an irregular singular point of x^3*y"-xy'+y=0. Hence it has no ∞ solution of the form y=x^r*Σ anx^n in x>0. n=0 (b)If p∈R^2 is a stable center for the linearized plane system of x'=f(x) (where x∈R^2, and f(p)=0), then p is also a stable equilibrium of x'=f(x). --

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