Question

Tính 1-2-3+4+5-6-7+8+...+1989-1990-1991+1992+1993

Answer 1

A=1-2-3 +4+5-6-7+8 +.....+1993

\(A=A_1+1993\)

\(A_1=\left(1-2-3+4\right)+\left(5-6-7+8\right)+....+\left(1989-1990-1991+1992\right)\)\(A_1=0+0+0...+0\)

A=1993

Answer 2

\(A=1-2-3+4+5-6-7+8+...+1989-1990-1991+1992+1993\)

\(A=\left(1-2-3+4\right)+\left(5-6-7+8\right)+...+\left(1989-1990-1991+1992\right)+1993\)

\(A=0+0+...+0+1993\)

\(A=1993\)