Question

if x=2y+6 find x cube- 8 cube -36xy-216

Answer 1

${x}^{3} - {8}^{3} - 36xy - 216 \\ (2y + 6) ^{3} - 512 - 36(2y + 6)y - 216 \\ 4 {y}^{3} + 216 - 512 - 72 {y}^{2} - 216y \\ 4 {y}^{3} - 72 {y}^{2} - 216y - 296 \\ y(4 {y}^{2} - 72y - 216 - 296) \\ 4 {y}^{2} - 72y - 512 \\ {y}^{2} - 18y - 128$