Let a,b,c,x,y, and z be complex numbers such that a=x−2b+c,b=y−2c+a,c=z−2a+b. If xy+yz+zx=67 and x+y+z=2010, find the value of xyz.
A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.
Solution
Manipulate the equations to get a common denominator: a=x−2b+c⟹x−2=ab+c⟹x−1=aa+b+c⟹x−11=a+b+ca; similarly, y−11=a+b+cb and z−11=a+b+cc. Thus $x−11+y−11+z−11 =1 ⇒ (y-1)(z-1)+(x-1)(z-1)+(x-1)(y-1) =(x-1)(y-1)(z-1) ⇒ x y+y z+z x-2(x+y+z)+3 =x y z-(x y+y z+z x)+(x+y+z)-1 ⇒ x y z-2(x y+y z+z x)+3(x+y+z)-4 =0 ⇒ x y z-2(67)+3(2010)-4 =0 ⇒ x y z =-5892
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