Double brackets
Multiplying two brackets by making sure every term in the first bracket meets every term in the second.
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Analogy
Like a handshake round a table: everyone from group A shakes hands with everyone from group B.
Example
x^2 + 5x + 2x + 10= x^2 + 7x + 10
In practice
The area of a garden with sides (x + 2) and (x + 5) metres uses double brackets.
Practice
Flashcards
- Expand (x + 2)(x + 5).x^2 + 7x + 10.
Questions people ask
What does FOIL mean?
FOIL stands for First, Outer, Inner, Last. It lists the four multiplications in a double bracket. For (x + 2)(x + 5): x times x, x times 5, 2 times x, 2 times 5. A grid works too, and it always gives four terms to collect.
Why do double brackets give four terms?
Each of the two terms in the first bracket multiplies each of the two terms in the second, so 2 x 2 = 4 products. Two of them are often like terms and combine. That is why the middle result is usually a single x term.