Question

if x=2y+6 then find the value of x³-8y³-36xy-216

Answer 1

answer is zero okgwhs

Answer 2

Hey there !!!!!

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(x-2y) = 6

Cubing on both sides

(x-2y)³ = 6³

(a-b)³ = a³- 3a²b+3ab²-b³

Comparing (x-2y)³ with (a-b)³ a=x   b=2y

(x-2y)³ =6³

x³- 3x²*2y+3x(2y)²-(2y)³= 216

x³- 6x²y+12xy²-8y³=216

x³+6xy(2y-x)-8y³=216

2y-x = 6

So,

x³-6xy(2y-x)-8y³=216

x³-6xy*6-8y³=216

x³-36xy-8y³-216=0 

So, 

x³-8y³-36xy-216 = 0

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Hope this helped you..........