Question

If 2x + 3y = -5, prove that 8x^3 + y^3 - 30xy + 125 = 0

Answer 1

(2x)^3 + (y)^3 + (5)^3 - 3×2x×y×5
(2x+y+5)(4x^2+y^2+25 -2xy -5y -10x)

Are you sure with the question? It's supposed to be 2x+y = -5
If we go with my value then,

(-5+5)(4x...........-10x)
0 × (4x..........-10x)
0 [ anything multiplied with 0 is 0 ]