If $$a+b+c=9$$ and $$ab+bc+ca=-22$$, then the value of $$a^{3}+b^{3}+c^{3}-3abc$$ is:
a + b + c = 9
ab + bc + ca = -22
We need to find the value of a³ + b³ + c³- 3abc
We know,
a³ + b³ + c³- 3abc = ( a + b + c ) ( a² + b² + c² - ab - bc - ca )
Now we need to find the value of a² + b² + c²
We also know,
( a + b + c )² = a² + b² + c² + 2 ( ab + bc + ca )
Putting the value of a + b + c = 9 and ab + bc + ca = -22
( 9 )² = a² + b² + c² + 2 ( -22 )
81 = a² + b² + c² -44
a² + b² + c² = 81 + 44
a² + b² + c² = 125
Now,
Substituting value in the formula for a³ + b³ + c³- 3abc
a³ + b³ + c³- 3abc = ( a + b + c ) ( a² + b² + c² - ab - bc - ca )
a³ + b³ + c³- 3abc = ( a + b + c ) ( a² + b² + c² - ( ab + bc + ca ) )
a³ + b³ + c³- 3abc = ( 9 ) ( 125 - ( =22) )
a³ + b³ + c³- 3abc = ( 9 ) ( 147 )
a³ + b³ + c³- 3abc = 1323
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