if 5x+3y=16 and xy=2, find the value of 125x3 + 27y3
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13
Answer:
★Given:-
- 5x + 3y = 16
- xy = 2
★To find:-
- 125x³ + 27y³
★Solution:-
125x³ = (5x)³ & 27y³ = (3y)³
=> 125x³ + 27y³ = (5x)³ + (3y)³
a³+b³=(a+b)(a²-ab+b²)
Here, a = 5x & b = 3y
=> (5x)³ + (3y)³ = (5x + 3y) ( (5x)² - 5x*3y + (3y)² )
=> (5x)³ + (3y)³ = 16 ( (5x)² - 15xy + (3y)² )
Adding and subtracting 30xy, we get
=> (5x)³ + (3y)³ = 16 ( (5x)² - 15xy + (3y)² + 30xy - 30xy )
=> (5x)³ + (3y)³ = 16 ( (5x)² + 30xy + (3y)² - 15xy - 30xy )
=> (5x)³ + (3y)³ = 16 ( (5x)² + 30xy + (3y)² - 45xy )
=> (5x)³ + (3y)³ = 16 ( (5x+3y)² - 45xy )
=> (5x)³ + (3y)³ = 16 ( (16)² - 45(2) )
=> (5x)³ + (3y)³ = 16 ( 256 - 90 ) = 16 (166) =
2656
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