Question

[Nguyễn Lan Hương]

Tính B , biết B = 1 - 4 + 7 - 10 + 13 - ... + 307 - 310 - 313 .

Answer 1

[Nguyễn Huy Tú]

\(B=1-4+7-10+...+307-310-313\)

\(\Rightarrow B=\left(1-4\right)+\left(7-10\right)+...+\left(307-310\right)-313\) ( 52 cặp số )

\(\Rightarrow B=-3+\left(-3\right)+...+\left(-3\right)-313\)

\(\Rightarrow B=\left(-3\right).52-313\)

\(\Rightarrow B=-156-313\)

\(\Rightarrow B=469\)

Vậy B = 469

Answer 2

[Ngô Tấn Đạt]

\(B=1-4+7-10+13-16+.....+307-310-313\\ \Rightarrow B=\left(1-4\right)+\left(7-10\right)+\left(13-16\right)+....+\left(307-310\right)-313\\ \Rightarrow B=\left(-3\right)+\left(-3\right)+....+\left(-3\right)-313\\ \Rightarrow B=\left(-3\right).52-313\\ \Rightarrow B=-156-313=-469\)