đây mà là toán 8 hả bn

1.

145+55=200

13+50+37=100

92+56-48=100

2.\(6x+x^2=-9\Leftrightarrow x\left(6+x\right)=-9\Leftrightarrow\hept{\begin{cases}x=-9\\6+x=-9\end{cases}\Leftrightarrow\hept{\begin{cases}x=-9\\x=-15\end{cases}}}\)

k mk nhé

  ( x +2 )² - ( x - 2 ) ( x + 2 )

= x² + 4x + 4 - x² - 4

= 4x

Hk tốt

\(\left(x+2\right)^2-\left(x-2\right)\left(x+2\right)\)

\(=x^2+4x+4-\left(x^2-4\right)\)

\(=x^2+4x+4-x^2+4\)

\(=4x+8\)

Ta có:

\(\left(x-y\right)^2+\left(y-z\right)^2+\left(z-x\right)^2=\left(y+z-2x\right)^2+\left(z+x-2y\right)^2+\left(x+y-2z\right)^2\)

\(\Rightarrow2x^2+2y^2+2z^2-2xy-2yz-2zx=6x^2+6y^2+6z^2-6xy-6yz-6zx\)

\(\Rightarrow4x^2+4y^2+4z^2-4xy-4yz-4zx=0\)

\(\Rightarrow2x^2+2y^2+2z^2-2xy-2yz-2zx=0\)

\(\Rightarrow\left(x-y\right)^2+\left(y-z\right)^2+\left(z-x\right)^2=0\)

\(\Rightarrow\hept{\begin{cases}\left(x-y\right)^2=0\\\left(y-z\right)^2=0\\\left(z-x\right)^2=0\end{cases}}\Rightarrow x=y=z\)

nhầm đa thức nhé

       \(x^2+y^2-2xy+x-y+1\)

\(=\left(x-y\right)^2+2\left(x-y\right).\frac{1}{2}+\frac{1}{4}+\frac{3}{4}\)

\(=\left(x-y+\frac{1}{2}\right)+\frac{3}{4}>0\forall x;y\)

Chúc bạn học tốt.

=0 nha

Sau bao nhiêu cộng trừ 8 thì ...

Cưới cx vẫn trở về con số 0

..army2k6

0 bn nhe.k nha