find the value of x³ + y ³ + 15 xy - 125 if x + y = 5
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Heya
_______________________________
x + y = 5
Cubing both sides
( x + y )³ = 125
=>
x³ + y³ + 3xy ( x + y ) - 125 = 0
=>
x³ + y³ + 3xy ( 5 ) - 125 = 0
=>
x³ + y³ + 15xy -125 = 0
_______________________________
x + y = 5
Cubing both sides
( x + y )³ = 125
=>
x³ + y³ + 3xy ( x + y ) - 125 = 0
=>
x³ + y³ + 3xy ( 5 ) - 125 = 0
=>
x³ + y³ + 15xy -125 = 0
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