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Answer 1 · 2018-01-07T05:35:29

#16y^3#

#x^3+8y^3-36xy-216# when #x=2y+6#

Substitute in #x=2y+6#

The expression becomes

#(2y+6)^3+8y^3-36y(2y+6)-216#

#=8y^3+72y^2+216y+216+8y^3-72y^2-216y-216#

Now, we can combine like-terms.

#=8y^3+cancel72y^2+cancel216y+cancel216+8y^3-cancel72y^2-cancel216y-cancel216#

#=16y^3#

Answer 2 · 2018-01-07T05:42:55

0

To find the value of an expression, we need to have a single variable.

We can do that by looking at the expression #x^3+8y^3-36xy-216#, and replacing every x with #2y+6#, since #x=2y+6#

#x^3+8y^3-36xy-216#

#(2y+6)^3+8y^3-36(2y+6)y-216#

#(8y^3+72y^2+216y+216)+8y^3+(-72y^2-216y)-216#

Then simplify by combining like terms.

#16y^3#

Isolate y to find value

#16y^3=0#

#(16y^3)/16=0/16#

#∛(y^3)=∛0#

#y=0#

Value is therefore 0