Question

Tính hợp lý:

A= 1-2-3+4+5-6-7+8+9-...+1992+1993-1994

Answer 1

\(\text{A= 1-2-3+4+5-6-7+8+9-...+1992+1993-1994}\)

\(A=\left(1-2-3+4\right)+...+\left(1989-1990-1992+1992\right)+1993-1994\)

\(A=0+0+...+0+1993-1994\)

\(A=-1\)

Answer 2

\(A=1-2-3+4+5-6-7+8+...+1992+1993-1994\)

\(A=\left(1-2-3+4\right)+...+\left(1989-1990-1991+1992\right)+1993-1994\)( 498 nhóm dư 2 )

\(A=0+0+...+0+1993-1994\)

\(A=1993-1994=-1\)

Vậy A = -1

Answer 3

Ta có :

A = 1-2-3+4+5-6-7+8+9-.....+1992+1993-1994

=> A = (1-2-3+4) + (5-6-7+8) + .....+ (1989-1990-1991+1992) + 1993 - 1994

= 0 + 0 + ...... + 0 + 1993 - 1994

= 0 + 1993 - 1994

= -1

Vậy A = -1