Question

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

Answer 1

${(x + y)}^{3} = {x}^{3} + {y}^{3} + 3xy(x + y)$

Consider

${(2x + y)}^{3} = 8 {x}^{3} + {y}^{3} + 6xy(2x + y)$

$- 125 = 8 {x}^{3} + {y}^{3} - 30xy$

$8 {x}^{3} + {y}^{3} - 30xy + 125 = 0$

Hope it helps

Answer 2

Step-by-step explanation:

(2x+y)^3= -5^3

8x^3 + y^3 + 6xy(2x+y) = -125

8x^3 + y^3 + 6xy(-5) = 125

hence proved.