Đáp án:
$-\dfrac{1}{2}$
Giải thích các bước giải:
$b)\bigg(2\sqrt[]{28}-3\sqrt[]{175}+4\sqrt[]{63}-7\sqrt[]{2\dfrac{2}{7}}\bigg):6\sqrt[]{7}$
$=\bigg(2\sqrt[]{2^2.7}-3\sqrt[]{5^2.7}+4\sqrt[]{3^2.7}-7\sqrt[]{\dfrac{16}{7}}\bigg).\dfrac{1}{6\sqrt[]{7}}$
$=(4\sqrt[]{7}-15\sqrt[]{7}+12\sqrt[]{7}-4\sqrt[]{7}).\dfrac{1}{6\sqrt[]{7}}$
$=(-3\sqrt[]{7}).\dfrac{1}{6\sqrt[]{7}}$
$=-\dfrac{1}{2}$