Question

Tính

a/ \(\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)

b/ A= \(\left(\frac{1}{2^2}-1\right).\left(\frac{1}{3^2}-1\right)....\left(\frac{1}{2013^2}-1\right).\left(\frac{1}{1014^2}-1\right)\)

   B=\(\frac{-1}{2}\) 

So sánh A và B

Answer 1

A = \(\left(\frac{1}{2^2}-1\right)\left(\frac{1}{3^2}-1\right)...\left(\frac{1}{2014^2}-1\right)\)

A = \(\left(-\frac{1.3}{2.2}\right)\left(-\frac{2.4}{3.3}\right)...\left(-\frac{2013.2015}{2014.2014}\right)\)

A = \(-\left[\frac{\left(1.2....2013\right)\left(3.4....2015\right)}{\left(2.3....2014\right)\left(2.3...2014\right)}\right]\)

A = \(-\left(\frac{2015}{2014.2}\right)\)

A = \(-\frac{2015}{4028}\)

Answer 2

còn câu b thì sao z mấy bn?