Question

TÍNH NHANH:

(-2)+4+(-6)+8+........+(-18)+20

2-4-6+8+10-12-14+16..........+1994-1996-1998+2000

Answer 1

\(\left(-2\right)+4+\left(-6\right)+8+...+\left(-18\right)+20\)

\(=\left[\left(-2\right)+4\right]+\left[\left(-6\right)+8\right]+...+\left[\left(-18\right)+20\right]\)(có 5 cặp)

\(=2+2+...+2\)

\(=2.5\)

\(=10\)

Answer 2

\(2-4-6+8+10-12-14+16+...+1994-1996-1998+2000\)\(=\left(2-4-6+8\right)+\left(10-12-14+16\right)+...+\left(1994-1996-1998+2000\right)\)\(=0+0+...+0\)

\(=0\)