Are you aware of the time?

Columbus discovered America

TH1: x+y+z=0

\(\Rightarrow\left\{{}\begin{matrix}x+y=-z\\y+z=-x\\z+x=-y\end{matrix}\right.\Rightarrow\dfrac{x+y}{z}=\dfrac{y+z}{x}=\dfrac{x+z}{y}=-1\)

TH2:\(x+y+z\ne0\)

Áp dụng tc dãy tỉ số bằng nhau ta có:

\(\dfrac{x+y}{z}=\dfrac{y+z}{x}=\dfrac{z+x}{y}=\dfrac{2\left(x+y+z\right)}{x+y+z}=2\)Vậy.....

\(A=2-5+8-11+...+98-101\)

\(=\left(2-5\right)+\left(8-11\right)+...+\left(98-101\right)\)

\(=\left(-3\right)+\left(-3\right)+...+\left(-3\right)\)(có 17 số -3)

\(=17.\left(-3\right)\)

\(=-51\)

ngu vcl