Expanding double brackets

Example: Expand (x - 4)(x - 2) using the grid method

Draw a grid with two rows and two columns, since we have two terms in each set of brackets:

\timesx-2
x
-4

Now, multiply each term in the first set of brackets by each term in the second set of brackets (with the grid method, this is as simple as filling in each box by multiplying the row and column headers):

\timesx-2
xx^2-2x
-4-4x8

Remember: The -2 and -4 headers multiply to give positive 8,

Add the terms in the middle of the grid together to get the final answer:

flashcards

QuestionAnswer
x^2x^2
-2x-2x
-4x-4x
88
How do you expand (x - 4)(x - 2) using the grid method?Draw a 2x2 grid, multiply each term from the first bracket by each term from the second, then sum the products: x^2 - 4x - 2x + 8 = x^2 - 6x + 8
What do you multiply to get 8 in the grid expansion of (x - 4)(x - 2)?Multiply -4 by -2, giving positive 8
What is the final expanded form of (x - 4)(x - 2)?x^2 - 6x + 8