Question

Tính nhanh

1/15 - 2/15 + 3/15 - 4/15 + 5/15 -6/15+7/15-8/15+9/15

Answer 1

\(\dfrac{1}{15}-\dfrac{2}{15}+\dfrac{3}{15}-\dfrac{4}{15}+\dfrac{5}{15}-\dfrac{6}{15}+\dfrac{7}{15}-\dfrac{8}{15}+\dfrac{9}{15}\)

\(=\dfrac{1-2+3-4+5-6+7-8+9}{15}\)

\(=\dfrac{\left(1-2\right)+\left(3-4\right)+\left(5-6\right)+\left(7-8\right)+9}{15}\) => có 4 cặp

\(=\dfrac{\left(-1\right)+\left(-1\right)+\left(-1\right)+\left(-1\right)+9}{15}\)

\(=\dfrac{\left(-1\right).4+9}{15}\)

\(=\dfrac{\left(-4\right)+9}{15}\)

\(=\dfrac{5}{15}=\dfrac{1}{3}\)