You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser.
Theo đề bài , ta có :
$ax + by + cz = 0$ \Rightarrow $(ax + by + cz)^2=0$
\Rightarrow $a^2x^2 + b^2y^2 + c^2z^2 + 2ax.by + 2ax.cz + 2by.cz = 0$
\Rightarrow$ a^2x^2 + b^2y^2 + c^2z^2 = - (2abxy + 2aczx + 2bcyz)$
Lại có :
$bc.(y-z)^2+ac.(x-z)^2+ab.(x-y)^2$
$= bc( y^2 - 2yz + z^2) + ac( x^2 - 2xz + z^2) + ab( x^2 - 2xy + y^2)$
$= bcy^2 + bcz^2 - 2bcyz + acx^2 + acz^2 - 2acxz + abx^2 + aby^2 - 2abxy$
$= (bcy^2 + bcz^2 + acx^2 + acz^2 + abx^2 + aby^2 ) - (2abxy + 2aczx + 2bcyz)$
$= bcy^2 + bcz^2 + acx^2 + acz^2 + abx^2 + aby^2 + a^2x^2 + b^2y^2 + c^2z^2$
$= ( a + b + c )( a.x^2+b.y^2+c.z^2)$
Thay vào là xong