Cho
M=x−(y−z)−2x+y+z−(2−x−y)N=x−[x−(y−2z)−2z]\begin{array}{l}M = x - (y - z) - 2{{x}} + y + z - (2 - x - y)\\N = x - \left[ {x - \left( {y - 2{{z}}} \right) - 2{{z}}} \right]\end{array}M=x−(y−z)−2x+y+z−(2−x−y)N=x−[x−(y−2z)−2z]
Tính M – N
-2z + 2
-2x – 2y – 2
2z – 2
-2x + 2y - 2
Đáp án: <p>2z – 2</p>
Phương pháp giải:
Rút gọn M, N rồi tính M - N
Lời giải chi tiết:
Ta có:
M=x−(y−z)−2x+y+z−(2−x−y)=x−y+z−2x+y+z−2+x+y=y+2z−2N=x−[x−(y−2z)−2z]=x−(x−y+2z−2z)=x−x+y=ysuy ra M−N=y+2z−2−y=2z−2\begin{array}{l}M = x - \left( {y - z} \right) - 2{{x}} + y + z - \left( {2 - x - y} \right)\\ = x - y + z - 2{{x}} + y + z - 2 + x + y\\ = y + 2{{z}} - 2\\N = x - \left[ {x - \left( {y - 2{{z}}} \right) - 2{{z}}} \right]\\ = x - \left( {x - y + 2{{z}} - 2{{z}}} \right) = x - x + y = y\\ \text{suy ra } M - N = y + 2{{z}} - 2 - y = 2{{z}} - 2\end{array}M=x−(y−z)−2x+y+z−(2−x−y)=x−y+z−2x+y+z−2+x+y=y+2z−2N=x−[x−(y−2z)−2z]=x−(x−y+2z−2z)=x−x+y=ysuy ra M−N=y+2z−2−y=2z−2
