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Question
Use the formula to expand the following:
(3) (3n − 5)3
(3) (3n − 5)3
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Solution
We know that (x − y)3 = x3 − 3x2y + 3xy2 − y3.
Comparing (3n − 5)3 with (x − y)3 , we get:
x = 3n and y = 5
Substituting these in the above formula:
(3n − 5)3 = (3n)3 − 3 × (3n)2 × 5 + 3 × 3n × (5)2 − 53
= 27n3 − 135n2 + 225n − 125
Comparing (3n − 5)3 with (x − y)3 , we get:
x = 3n and y = 5
Substituting these in the above formula:
(3n − 5)3 = (3n)3 − 3 × (3n)2 × 5 + 3 × 3n × (5)2 − 53
= 27n3 − 135n2 + 225n − 125
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