x³ - 27y³-343-63xy when x= 3y+ 7 factorise using suitable identity pls answer its urgent........
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Answer:
x³ - 27y³- 343 - 63xy - 343, where x = 3y + 7
= 189xy² + 378
Step-by-step explanation:
f(x) = x³ - 27y³- 343 - 63xy - 343
x = 3y + 7 ( Given )
Substituting x = 3y + 7 in f(x), we get
(3y + 7)³ - 27y³- 63xy - 343
(a + b)³ = a³ + b³ + 3ab(a + b)
So, we get
27y² + 343 + 63xy( 3y + 7 ) - 27y³ - 63xy - 343
=> 63xy( 3y + 7 ) - 63xy
=> 63xy ( 3y + 7 - 1 )
= 63xy ( 3y + 6 )
= 189xy² + 378
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