How many Triple?

Algebra Level 5

How many Triple T = ( x y , y z , z x ) T=(x-y,y-z,z-x) there is such that :

  • x x , y y and z z are complex numbers
  • x ( x 1 ) + 2 y z = y ( y 1 ) + 2 z x = z ( z 1 ) + 2 x y x(x-1)+2yz=y(y-1)+2zx=z(z-1)+2xy


The answer is 4.

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1 solution

If we take ([T=(a, b, c)), we got a + b + c = x y + y z + z x = 0 a+b+c=x-y+y-z+z-x=0 so b = ( a + c ) b=-(a+c)

Let r C r\in\mathbb{C} , x = x + r , y = y + r , z = z + r x'=x+r, y'=y+r, z'=z+r , then a = x y , b = y z , c = z x a=x'-y', b=y'-z', c=z'-x' So we can suppose x = x x = 0 x'=x-x=0 , and then x = 0 , y = a , z = c x'=0, y'=-a, z'=c And the equallity become 2 a c = a ( a 1 ) = c ( c 1 ) -2ac=-a(-a-1)=c(c-1) 2 a c = a ( a + 1 ) = c ( c 1 ) -2ac=a(a+1)=c(c-1) If c = 0 c=0 then a ( a + 1 ) = 0 a(a+1)=0

So the possible solutions are T = ( 0 , 0 , 0 ) T=(0, 0, 0) T = ( 1 , 1 , 0 ) T=(-1, 1, 0) Else c 0 c\neq0 and 2 a c = c ( c 1 ) -2ac=c(c-1)

So 2 a = c 1 -2a=c-1 ; c = 1 2 a c=1-2a

Taking the equallity a ( a + 1 ) = c ( c 1 ) a(a+1)=c(c-1) we have a 2 + a = 4 a 2 2 a a^2+a=4a^2-2a 3 a 2 = 3 a 3a^2=3a So, the possible solutions are T = ( 0 , 1 , 1 ) T=(0, -1, 1) T = ( 1 , 0 , 1 ) T=(1, 0, -1)

Then, the answer is n = 4 \boxed{n=4}

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