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Edexcel A-level Maths Manipulating equations

Manipulating equations

This page covers the following topics:

1. Expanding binomials using grids
2. Order of binomial expansions
3. Factorising quadratics
4. Partial fractions

One way to expand binomials is by using grids. To do this, assign the terms of the first bracket to the boxes of the grid vertically and assign the terms of the second bracket to the boxes of the grid horizontally. Fill out the grid by multiplying the terms assigned to each box and take the sum of all the products. This will give the expansion of the two brackets.

Expanding binomials using grids

Another way to expand binomials is to use the method of FOIL to determine the order of expansion. FOIL stands for first, outer, inner and last and helps remember the terms that must be multiplied together to find an expansion of two brackets. FOIL method suggests to multiply the two first terms of the brackets, the ones on the outer side of the brackets, the ones on the inner side of the brackets and the two last terms of the brackets. Taking the sum of the products gives the expansion of the two brackets.

Order of binomial expansions

Factorising is the reverse of expanding. A quadratic expression, xΒ² + ax + b, can be factorised to be written as (x + c)(x + d), where the sum of c and d is equal to a and the product of c and d is equal to b. A special case of factorisation, called the difference between the two squares, is given as: xΒ² βˆ’ yΒ² = (x βˆ’ y)(x + y).

Factorising quadratics

Algebraic rational functions can be written as a sum or difference of fractions; this is called partial fractions. To do this, the general forms given in the image can be used. The new fractions can then be added by finding common denominators and coefficients of respective powers of variables equated to get simultaneous equations. An example of splitting a fraction into partial fractions is provided below.

(5x + 7)/(x + 3)(x + 2) = A/(x + 3) + B/(x + 2)
multiplying by (x + 3)(x + 2): 5x + 7 = A(x + 2) + B(x + 3)
expanding: 5x + 7 = Ax + 2A + Bx + 3B
collecting like terms: 5x + 7 = x(A + B) + 2A + 3B
equating coefficients of x: 5 = A + B
equating constants: 7 = 2A + 3B
solving simultaneously: A = 8 and B = βˆ’3
(5x + 7)/(x + 3) (x + 2) = 8/(x + 3) βˆ’ 3(x + 2)

Partial fractions

1

Multiply out brackets (14 βˆ’ x)(8x + 9) by using the grid method.

Multiply out brackets (14 βˆ’ x)(8x + 9) by using the grid method.

2

Give (15x βˆ’ 1)/(5x + 1)Β² as partial fractions.

Give (15x βˆ’ 1)/(5x + 1)Β² as partial fractions.

3

An ornament is shaped and sized as shown in the diagram. Find the perimeter of the ornament in its simplest, factorised form. The perimeter of a shape is the sum of the lengths of its sides.

An ornament is shaped and sized as shown in the diagram. Find the perimeter of the ornament in its simplest, factorised form. The perimeter of a shape is the sum of the lengths of its sides.

4

Express (16x + 52)/(2x + 7)Β² as partial fractions.

Express (16x + 52)/(2x + 7)Β² as partial fractions.

5

Using the FOIL method to simplify (8w + 5)(7 βˆ’ wΒ²) + 36w and then find its value when w = 25.

Using the FOIL method to simplify (8w + 5)(7 βˆ’ wΒ²) + 36w and then find its value when w = 25.

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