Question

1. Tính:

1 - 2 - 3 + 4 + 5 - 6 - 7 + ... + 97 - 98 - 99 +100

2. Tìm x, y là số nguyên:

xy - 3x + 7y = 21

Giúp mih vs nha m.n T-T

Answer 1

Bài 2:

\(xy-3x+7y=21\)

\(\Rightarrow x\left(y-3\right)+7y-21=0\)

\(\Rightarrow x\left(y-3\right)+7\left(y-3\right)=0\)

\(\Rightarrow\left(x+7\right)\left(y-3\right)=0\)

\(\Rightarrow\left\{\begin{matrix}x+7=0\\y-3=0\end{matrix}\right.\Rightarrow\left\{\begin{matrix}x=-7\\y=3\end{matrix}\right.\)

Vậy \(\left\{\begin{matrix}x=-7\\y=3\end{matrix}\right.\)

Answer 2

Bài 1:

\(1-2-3+4+5-6-7+...+97-98-99+100\)

\(=\left(1-2-3+4\right)+\left(5-6-7+8\right)+...+\left(97-98-99+100\right)\)

\(=0+0+0+...+0+0+0\)

\(=0\)