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Question
If 5x – 4y = 7 and xy = 8, find : 125x3 – 64y3.
Sum
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Solution
125x3 − 64y3 = (5x)3 − (4y)3
= (5x − 4y)3 + 3(5x) (4y) (5x − 4y)
= (5x − 4y)3 + 60xy (5x − 4y)
= (7)3 + 60 (8) (7)
= 343 + 3360
= 3703
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