1
Question
Use the formula to expand the following:
(1) (x − 7)3
(1) (x − 7)3
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Solution
We know that (x − y)3 = x3 − 3x2y + 3xy2 − y3.
Comparing (x − 7)3 with (x − y)3, we get:
x = x and y = 7
Substituting these in the above formula:
(x − 7)3 = x3 − 3 × x3 × 7 + 3 × x × 72 − 73
= x3 − 21x2 + 147x − 343
∴ (x − 7)3 = x3 − 21x2 + 147x − 343
Comparing (x − 7)3 with (x − y)3, we get:
x = x and y = 7
Substituting these in the above formula:
(x − 7)3 = x3 − 3 × x3 × 7 + 3 × x × 72 − 73
= x3 − 21x2 + 147x − 343
∴ (x − 7)3 = x3 − 21x2 + 147x − 343
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