The Lesson
Expanding double brackets means removing brackets from a pair of expressions in brackets. Imagine we wanted to remove the brackets from the expression below. We have to expand the brackets. We can use the grid method to expand the brackets.Expanding Double Brackets Using the Grid Method
Look at the grid below. It is a rectangle. It represents (x + 1)(x + 2). Consider the entire rectangle. The height of the entire rectangle is x + 1.
 The width of the entire rectangle is x + 2.
 The area of the rectangle is the height × width. It is (x + 1)(x + 2).
 The height of the dark blue rectangle is x.
 The width of the dark blue rectangle is x.
 The area of the dark blue rectangle is x^{2}.
 The height of the light blue rectangle is x.
 The width of the light blue rectangle is 2.
 The area of the light blue rectangle is 2x.
 The height of the orange rectangle is 1.
 The width of the orange rectangle is x.
 The area of the orange rectangle is x.
 The height of the pink rectangle is 1.
 The width of the pink rectangle is 2.
 The area of the pink rectangle is 2.
(x + 1)(x + 2) = x^{2} + 2x + x + 2
A Real Example of How to Expand Double Brackets Using the Grid Method
Expanding brackets is easy. Expanding double brackets using the grid method is easy.Question
Expand the brackets below.StepbyStep:
1
Find the first term in the first brackets (x). Draw a vertical line and label its height with this term.
2
Find the second term in the first brackets (2). Draw a vertical line down from the vertical line already drawn. Label its height with this term.
3
Find the first term inside the second brackets (y). Draw a horizontal line from the vertical lines already drawn. Label its width with this term.
4
Find the second term inside the second brackets (3). Draw another horizontal line, following the horizontal line already drawn. Label its width with this term.
5
Draw the rest of the grid.
6
Find the area of each rectangle in the grid by multiplying the height and width of each rectangle.
The area of the first grid is its height (x) times its width (y).
x × y = xy
7
Find the area of each rectangle in the grid by multiplying the height and width of each rectangle.
The area of the second grid is its height (x) times its width (3).
x × 3 = 3x
8
Find the area of each rectangle in the grid by multiplying the height and width of each rectangle.
The area of the third grid is its height (2) times its width (y).
2 × y = 2y
9
Find the area of each rectangle in the grid by multiplying the height and width of each rectangle.
The area of the fourth grid is its height (2) times its width (3).
2 × 3 = 6
9
Add the areas of the rectangles in the grid.
xy + 3x + 2y + 6
Answer:
Expanding (x + 2)(y + 3) gives xy + 3x + 2y + 6.Multiplication Tips

Multiplying a number with a variable
2 × x = 2x
5 × x = 5x

Multiplying a number with a variable with a coefficient
2 × 2x = 4x
3 × 5x = 15x

Multiplying a variable with a variable
x × y = xy
x × x = x^{2}