Question

Biết b.z-c.y/a = c.x-a.z/b = a.y-b.x/(a,b,c khác 0) Chứng minh rằng x/y=y/b=z/c

Answer 1

\(\dfrac{bz-cy}{a}=\dfrac{cx-az}{b}=\dfrac{ay-bx}{c}\)

\(\Rightarrow\dfrac{abz-acy}{a^2}=\dfrac{bcx-abz}{b^2}=\dfrac{acy-bcx}{c^2}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{abz-acy}{a^2}=\dfrac{bcx-abz}{b^2}=\dfrac{acy-bcx}{c^2}=\dfrac{abz-acy+bcx-abz+acy-bcx}{a^2+b^2+c^2}=0\)

Suy ra \(\left\{{}\begin{matrix}bz=cy\Leftrightarrow\dfrac{y}{b}=\dfrac{z}{c}\\cx=az\Leftrightarrow\dfrac{x}{a}=\dfrac{z}{c}\\ay=bx\Leftrightarrow\dfrac{x}{a}=\dfrac{y}{b}\end{matrix}\right.\Leftrightarrow\dfrac{x}{a}=\dfrac{y}{b}=\dfrac{z}{c}\left(đpcm\right)\)

p/s: đã sửa đề