CHO X2− YZ = A Y , 2− = ZX B Z , 2− XY = C CMR

Bài 119: Cho x

2

yz = a y ,

2

− = zx b z ,

2

xy = c CMR : ax by cz + + = + + ( x y z a b c )( + + )

Với x y z , ,  0

HD:

 − =

3

x xyz ax

 − = = + + = + + −

  − =

3 3 3 3

3

y xyz by ax by cz x y z xyz

Từ gt=>

z xyz cz

( ) (

2 2 2

) ( )( )

= + + = + + + + − − − = + + + +

ax by cz x y z x y z xy yz zx x y z a b c

 + + =

2

x y

2 1 0

 + + =

  + + =

y z

, Tính A = x

2000

+ y

2000

+ z

2000