Edexcel A Level Further Maths: Core Pure:复习笔记8.1.1 Intro to Differential Equations

General Solutions

What is a differential equation?

8.3.1-Notes-des_egs

  • Any equation, involving a derivative term, is a differential equation
  • Equations involving only first derivative terms are called first order differential equations
  • Equations involving second derivative terms are called second order differential equations

What is a general solution?

8.3.1-Notes-des_gen_sol

  • Integration will be involved in solving the differential equation
    • ie working back to “y = f(x)”

     

  • A constant of integration, c is produced
  • This gives an infinite number of solutions to the differential equation, each of the form y = g(x) + c  (ie  y = f(x)  where  f(x) = g(x) + c)
    • … and the solution y= g(x) + c is called the general solutionThese are often called a family of solutions …

Worked Example

Find the general solution to the differential equation .

fm-8-1-1-diff-eqns-general-we-solution

 

Particular Solutions

What is a particular solution?

  • Ensure you are familiar with General Solutions first
  • With extra information, the constant of integration, c, can be found
  • This means the particular solution (from the family of solutions) can be found

8.3.2-Notes-ps_eg

What is a boundary condition/initial condition?

A boundary condition is a piece of extra information that lets you find the particular solution

  • For example knowing y = 4 when x = 0 in the preceding example
  • In a model this could be a particle coming to rest after a certain time, ie v = 0 at time t
  • Differential equations are used in modelling, experiments and real-life situations
  • A boundary condition is often called an initial condition when it gives the situation at the start of the model or experiment
  • This is often linked to time, so t = 0
  • It is possible to have two boundary conditions
    • eg a particle initially at rest has velocity, v = 0 and acceleration, a = 0 at time, t = 0
    • for a second order differential equation you need two boundary conditions to find the particular solution

     

Worked Example

The velocity of a particle, initially at rest, is modelled by the differential equation   , where is the velocity of the particle and  is the time since the particle began moving.

a) Find the velocity of the particle after 3 seconds.

fm-8-1-1-diff-eqns-particular-we-solution-a

b) Find the time at which the particle comes to rest for the second time.

al-fm-8-1-1-diff-eqns-we-solution-

 

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