Question
Factorise the following.
$ y^2+4 y-21 $
$ y^2+4 y-21 $
✓
Answer
$ y^2+4 y-21 $
$ =y^2+(7-3) y-21 $
$ =y^2+7 y-3 y-21 $
$ =y(y+7)-3(y+7) $
$ =(y+7)(y-3) $
$ =y^2+(7-3) y-21 $
$ =y^2+7 y-3 y-21 $
$ =y(y+7)-3(y+7) $
$ =(y+7)(y-3) $
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