Question

If x+y=5 then find the value of x^3+y^3+15xy-125

Answer 1

x+y=5
x=5-y (equation 1)
x³+y³+15xy-125
(5-y)³+y³+15(5-y)y-125
(125-y³-15y(5-y))+y³+75y-15y²-125
125-y³-75y+15y²+y³+75y-15y²-125

All the variables are same and of opposite signs... So they will be cancelled
Therefore... The answer will be 0