Question

Find the value of x3-8y3-36xy-216 when x= 2y+6

Answer 1

Putting value x=2y+6
(2y+6)whole cube-8y3-36y(2y+6)
8y3+216+72y2+216y-8y3-72y2-216-216y
0      (after cancelling)

Answer 2

Answer:

so given

x = 2y+6

⇒ x - 2y = 6      ...... (i)

cubing both sides

⇒ x³ - 8y³ - 6xy(x - 2y) = 216

⇒ x³ - 8y³ - 6xy(6) = 216      {since , x - 2y = 6 from i}

⇒x³ - 8y³ - 36xy - 216 = 0

so the value of  x³ - 8y³ - 36xy - 216 = 0  ANSWER