2/5 * ( -5/12 +-9/12 ) -2/5 * (4/13 - 5/12 ):2 khó ko cách bạn

Đáp án:

$-\dfrac{347}{780}$

Giải thích các bước giải:

$\dfrac{2}{5}\:.\:\left(\dfrac{-5}{12}+\dfrac{-9}{12}\right)-\dfrac{2}{5}\:.\:\left(\dfrac{4}{13}-\dfrac{5}{12}\right)\::\:2$

$=\dfrac{2}{5}\:.\:\left(-\dfrac{5}{12}-\dfrac{3}{4}\right)-\dfrac{2}{5}\:.\:\left(\dfrac{4}{13}-\dfrac{5}{12}\right)\::\:\:2$

$=\dfrac{2}{5}\:.\:\left(-\dfrac{7}{6}\right)-\dfrac{2}{5}\:.\:\left(-\dfrac{17}{156}\right)\::\:\:2$

$=-\dfrac{7}{15}-\dfrac{2}{5}\left(-\dfrac{17}{156}\right)\::\:\:2$

$=-\dfrac{7}{15}-\left(-\dfrac{17}{780}\right)$

$=-\dfrac{7}{15}+\dfrac{17}{780}$

$=-\dfrac{364}{780}+\dfrac{17}{780}$

$=\dfrac{-364+17}{780}$

$=-\dfrac{347}{780}$