Question

Find the value of :
(i)x³-8y³-36xy-216, when x = 2y+6

Answer 1

$x = 2y + 6 \: \: \: > > x - 2y = 6$
Given expression

$= {(x - 2y)}^{3} + 6xy(x - 2y) \\ - 36xy - 216$
$= {6}^{3} + 6xy(6) - 36xy - 216$
$= 216 + 36xy - 36xy - 216 \\ = 0$