Finding the Constant of Integration (DP IB Applications & Interpretation (AI)): Revision Note

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Finding the Constant of Integration

What is the constant of integration? 

  • When finding an anti-derivative there is a constant term to consider

    • This constant term, usually called c, is the constant of integration

  • In terms of graphing an anti-derivative, there are endless possibilities

    • Collectively these may be referred to as the family of antiderivatives or family of curves

      • They all have the same shape, but are just shifted up or down vertically compared to each other

      • Each one corresponds to a different possible value of c

  • The value of the constant of integration is determined by the exact location of the curve

    • if a point on the curve is known, the constant of integration can be found

How do I find the constant of integration?

  • For integral f left parenthesis x right parenthesis space straight d x equals straight F left parenthesis x right parenthesis plus c, the constant of integration, c, can be found if a point on the graph of y equals straight F left parenthesis x right parenthesis plus c is known 
     

  • STEP 1

     If need be, rewritespace f left parenthesis x right parenthesis into an integrable form

    Each term needs to be a power of x (or a constant)

     

  • STEP 2

     Integrate each term ofspace f left parenthesis x right parenthesis, remembering the constant of integration “plus c

      

  • STEP 3

    Substitute the x and y coordinates of a given point in to straight F left parenthesis x right parenthesis plus c to form an equation in c

    Solve the equation to find c

Examiner Tips and Tricks

If a question gives you extra information that allows the constant of integration can be found, be sure to find it. Don't just leave your answer with a "plus c".

Worked Example

The graph of y equals f left parenthesis x right parenthesis passes through the point left parenthesis 3 comma negative 4 right parenthesis.  The gradient function ofspace f left parenthesis x right parenthesis is given byspace f to the power of apostrophe left parenthesis x right parenthesis equals 3 x squared minus 4 x minus 4.

Findspace f left parenthesis x right parenthesis.

5-2-3-ib-sl-ai-aa-we1-soltn-

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