Question

Tính P= -1/20 + -1/30 + -1/42 + -1/56 + -1/72 + -1/90

Answer 1

\(P=\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)

\(P=\dfrac{-1}{4.5}+\dfrac{-1}{5.6}+\dfrac{-1}{6.7}+\dfrac{-1}{7.8}+\dfrac{-1}{8.9}+\dfrac{-1}{9.10}\)

\(P=\left(-1\right).\left(\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}\right)\)

\(P=\left(-1\right).\left(\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\right)\)

\(P=\left(-1\right).\left(\dfrac{1}{4}-\dfrac{1}{10}\right)\)

\(P=\left(-1\right).\left(\dfrac{5}{20}-\dfrac{2}{20}\right)\)

\(P=\left(-1\right).\dfrac{3}{20}=\dfrac{-3}{20}\)