\(A=1-2+3-4+...+97-98+99\)
\(A=\left(1-2\right)+\left(3-4\right)+...+\left(97-98\right)+99\)
\(A=-1+\left(-1\right)+...+\left(-1\right)+99\)
\(A=\left(-1\right).49+99\)
\(A=-49+99\)
\(A=50\)
A = 1 - 2 + 3 - 4 +…+ 97 - 98 + 99
A = ( 1 - 2 ) + ( 3 - 4 ) + ... + ( 97 - 98 ) + 99
A = ( -1 ) + ( -1 ) + ... + ( -1 ) + 99
A = ( -1 ) . 49 + 99
A = 50
\(A=1-2+3-4+...+97-98+99\)
\(A=\left(1-2\right)+\left(3-4\right)+...+\left(97-98\right)+99\)
\(A=\left(-1\right)+\left(-1\right)+...+\left(-1\right)+99\)
\(\Rightarrow A=\left(-1\right).49+99\)
\(\Rightarrow A=50\)
\(A=1-2+3-4+...-98+99\)
\(\Rightarrow A=\left(1-2\right)+\left(3-4\right)+...+\left(97-98\right)+99\)
\(\Rightarrow A=-1+\left(-1\right)+....+\left(-1\right)+99\)( Có 49 số -1)
\(\Rightarrow A=-1\cdot49+99\)
\(\Rightarrow A=-49+99\)
\(\Rightarrow A=50\)
VẬy A=50
