Edexcel A Level Further Maths: Core Pure:复习笔记3.2.1 Sums of Integers, Squares & Cubes

Sums of Integers, Squares & Cubes

How can we use sigma notation?

  • When writing the sum of a series you can use sigma notation
    • The series  can instead be written as
    • This means “the sum of all the terms from  to for the sequence described by "
    • would mean
  • Using the following relations, summations can be grouped together (or ungrouped) to make some calculations easier:

  • a and b are constants, and  and  are a functions of r
  • Note that the top and bottom summation limits ( ) are the same for all the sums
    • This is important – if the top and bottom limits don’t all match then the relation is no longer valid!
  • This can be very useful when as are straightforward to find using formulae
  • A useful result to remember is that

What are the formulae for finding sums of integers, squares, and cubes?

  • There are several useful formulae for summing integers, square numbers, and cube numbers
  • The sum of the first  natural numbers is given by
      • This formula is not given in the formula book
  • The sum of the first  square numbers is given by
      • This formula is given in the formula book
  • The sum of the first  cube numbers is given by
      • This formula is given in the formula book
      • Notice that this is equal to the formula for the sum of the first  natural numbers, squared
  • Using the relations given above, a more complicated summation can often be broken down into sums of constants, natural numbers, squares, and cubes
    • For example,

Exam Tip

  • You can find summations using sigma notation on most advanced scientific calculators or graphics calculators – you can use this to check your answers
  • Bear in mind, however, that the question will normally require you to show your full working

Worked Example

Find

 

3-2-1-edx-a-fm-we1a-soltn

 

转载自savemyexams

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