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Question
If x + 5y = 10; find the value of x3 + 125y3 + 150xy − 1000.
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Solution
Given
⇒ x + 5y = 10
Cubing both sides we get:
⇒ (x + 5y)3 = 103
⇒ x3 + (5y)3 + 3 × x × 5y × (x + 5y) = 1000
⇒ x3 + 125y3 + 15xy × 10 = 1000
⇒ x3 + 125y3 + 150xy − 1000 = 0
Hence, x3 + 125y3 + 150xy − 1000 = 0
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