27y³-(2x-3y)³ factorise
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(a+b)
3
−(a−b)
3
=a
3
+b
3
+3a
2
b+3ab
2
−(a
3
−b
3
−3a
2
b+3ab
2
)
=2b
3
+6a
2
b
=2b(b
2
+3a
2)
Thus
(2x+3y)
3
−(2x−3y)
3
=3y((3y)
2
+3⋅(2x)
2
)=3y(9y
2
+12x
2)
=9y(3y
2
+4x
2)
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