Question

Tính tổng:

a) 1 + (-3) + 2 + (-4) + 3 + (-5) +... +18 + (-20)

b) -1 + 2 - 3 + 4 - 5 + 6 -... + 2017+ 2018

cho mik xin lời giải chi tiết vs ạ

Answer 1

1: =(-2)+(-2)+...+(-2)

=-2*18

=-36

2: =(-1+2)+(-3+4)+...+(-2017+2018)

=1+1+...+1

=1009

Answer 2

\(a).1+\left(-3\right)+2+\left(-4\right)+3+\left(-5\right)+...+18+\left(-20\right)\)

\(=\left[1+\left(-3\right)\right]+\left[2+\left(-4\right)\right]+...+\left[18+\left(-20\right)\right]\)

\(=\left(-2\right)+\left(-2\right)+\left(-2\right)+...+\left(-2\right)\)

\(=\left(-2\right).18=-36\)

 

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\(b).-1+2-3+4-5+6-...+2017+2018\)

\(=\left(-1+2\right)+\left(-3+4\right)+\left(-5+6\right)+...+\left(-2017+2018\right)\)

\(=1+1+1+1+.....+1\)

\(=1.1009=1009\)

Answer 3

1: =(-2)+(-2)+...+(-2)

=-2*18

=-36

2: =(-1+2)+(-3+4)+...+(-2017+2018)

=1+1+...+1

=1009