a 2 ( a 9 9 9 9 8 + 1 ) + b 2 ( b 9 9 9 9 8 + 1 ) + c 2 ( c 9 9 9 9 8 + 1 ) = 2 ( a 5 0 0 0 0 b + b 5 0 0 0 0 c + c 5 0 0 0 0 a )
How many ordered triples ( a , b , c ) are there where a , b and c are complex numbers and a 5 0 0 0 0 − b , b 5 0 0 0 0 − c and c 5 0 0 0 0 − a are rational numbers satisfying the equation above?
The answer can be expressed in the form x × 1 0 1 0 .
Find the value of x .
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Why should rational numbers be equal to 0? Please explain, thanks
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Square of a Rational Number is either 0 or a positive value. Since their sum is equal to 0 , they all must be 0 .
you got a^124999999999999=1 hence one root of a=1 must be neglected so there are 124999999999998 complex roots
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a = 1 will not be neglected because 1 is also a complex number.
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Expanding the brackets and transferring all the terms to one side, we get:
a 1 0 0 0 0 0 + a 2 + b 1 0 0 0 0 0 + b 2 + c 1 0 0 0 0 0 + c 2 − 2 a 5 0 0 0 0 b − 2 b 5 0 0 0 0 c − 2 c 5 0 0 0 0 a = 0
Rearranging the terms, we get:
( a 5 0 0 0 0 − b ) 2 + ( b 5 0 0 0 0 − c ) 2 + ( c 5 0 0 0 0 − a ) 2 = 0 .
We can deduce from here that each and every term of the above equation is equal to zero as they are rational.
So, a 5 0 0 0 0 = b , b 5 0 0 0 0 = c and c 5 0 0 0 0 = a .
By substitution, we get:
( ( a 5 0 0 0 0 ) 5 0 0 0 0 ) 5 0 0 0 0 ) = a .
a 1 2 5 0 0 0 0 0 0 0 0 0 0 0 0 = a .
Clearly, a = 0 is a solution to this equation.
Now consider the case when a = 0 :
We can divide both sides by a to get a 1 2 4 9 9 9 9 9 9 9 9 9 9 9 9 = 1 .
Now, we get 1 2 4 9 9 9 9 9 9 9 9 9 9 9 9 complex roots of unity and 1 solution when a = 0 .
So, in all there are 1 2 5 0 0 0 0 0 0 0 0 0 0 0 0 ordered triplets which can be represented as 1 2 5 0 0 × 1 0 1 0 .
Hence, our final answer is 1 2 5 0 0 .