Question

tính hợp lí

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

Answer 1

A = (1/3 - 8/15 - 1/7 ) + [ 2/3 + (-7/5) + 1/1/7]

= (1/3 - 8/15 - 1/7) + [ 2/3 + (-7/5) + 8/7 ]

= 1/3 - 8/15 - 1/7 + 2/3 + (-7/5) + 8/7

= ( 1/3 + 2/3 ) + [ -8/15 + (-7/5) ] + ( -1/7 +8/7 )

= 1 + [-8/15 + (-21/15) + 1

= 1 + (-29/15) + 1

= 15/15 + (-29/15) + 15/15

= 1/15

Answer 2

\(A=\left(\dfrac{1}{3}-\dfrac{8}{15}-\dfrac{1}{7}\right)+\left(\dfrac{2}{3}+\dfrac{-7}{5}+1\dfrac{1}{7}\right)\)

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

\(=\left(\dfrac{1}{3}-\dfrac{8}{15}+\dfrac{2}{3}-\dfrac{7}{5}\right)+\left(-\dfrac{1}{7}+\dfrac{8}{7}\right)\)

\(=\left(\dfrac{5}{15}-\dfrac{8}{15}+\dfrac{10}{15}-\dfrac{21}{15}\right)+1\)

\(=\left(-\dfrac{14}{15}\right)+1\)

\(=-\dfrac{14}{15}+\dfrac{15}{15}\)

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