
Factorising is the inverse of multiplying out the brackets. It's the process of taking a string of terms and regrouping them as expressions mulitplied together. You should remember from Intermediate 2 that there are three types of factors:
common factors
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difference of two squares
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trinomials
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These factors can be also applied to trigonometric expressions, that is, expressions involving involving sin x, cos x and tan x. For example:
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Remember that you can multiply out the brackets to check that you've not altered the original expression.