Question

1, 1+( -2)+3+(-4) + ........ + 19 + ( -20 )

2, 1-2+3-4+....... + 99-100

3, 2-4+6-8+.......+48-50

4, -1+3-5+7-.......+97-99

5, 1+2-3-4+......+97+98-99-100

Tick ai đầu tien nhé

Thank you bạn nhiều

Answer 1

1) \(1+\left(-2\right)+3+\left(-4\right)+...+19+\left(-20\right).\)

\(=\left[1+\left(-2\right)\right]+\left[3+\left(-4\right)\right]+...+\left[19+\left(-20\right)\right].\)

\(=-1+\left(-1\right)+...+\left(-1\right)\) (10 số hạng -1).

\(=-1.10=-10.\)

Vậy..........

2); 3); 4): làm tương tự 1).

5) \(1+2-3-4+...+97+98-99-100.\)

\(=1+\left(2-3-4+5\right)+\left(6-7-8+9\right)...+\left(94-95-96+97\right)+\left(98-99-100\right).\)

\(=1+0+0+...+0+\left(-101\right).\)

\(=1+\left(-101\right).\)

\(=-100.\)

Vậy..........