Question

1 Thực hiện phép tính:

a)\(-\dfrac{1}{2}+\dfrac{2}{3}-\dfrac{3}{4}+\dfrac{4}{5}\) b)\(\dfrac{1}{2}+\dfrac{2}{9}-\dfrac{3}{5}-\dfrac{4}{5}\)

Answer 1

\(a.\)

\(-\dfrac{1}{2}+\dfrac{2}{3}-\dfrac{3}{4}+\dfrac{4}{5}\)

\(=\left(-\dfrac{1}{2}-\dfrac{3}{4}\right)+\left(\dfrac{2}{3}+\dfrac{4}{5}\right)\)

\(=\left(-\dfrac{2}{4}-\dfrac{3}{4}\right)+\left(\dfrac{10}{15}+\dfrac{12}{15}\right)\)

\(=-\dfrac{5}{4}+\dfrac{22}{15}=\dfrac{13}{60}\)

\(b.\)

\(\dfrac{1}{2}+\dfrac{2}{9}-\dfrac{3}{5}-\dfrac{4}{5}\)

\(=\dfrac{1}{2}+\dfrac{2}{9}-\dfrac{7}{5}\)

\(=\dfrac{45}{90}+\dfrac{20}{90}-\dfrac{126}{90}=-\dfrac{61}{90}\)