Expanding and factoring are two opposite skills in algebra.
When you expand, you remove the brackets by multiplying each term inside by the number or variable outside — this is called using the distributive property.
When you factor, you do the reverse — you find the common factor and put the expression back into brackets.
Examples:
Expanding:
3(𝑥+4)=3𝑥+12
Factoring:
6𝑥+9=3(2𝑥+3)
