Câu hỏi:

\(\frac{9}{{15}}.\)

\(\frac{{27}}{{125}}.\)

\(\frac{{ - 9}}{{15}}.\)

\(\frac{{ - 27}}{{125}}.\)

\(a - b + c + d = 0.\)

\(a = b + c + d.\)

\(b = d - a - c.\)

\(c = b - a + d.\)

\(2,3.\)

\(3,7557.\)

\( - 0,25.\)

\( - 6,12\left( {63} \right).\)

Số tự nhiên

\(\sqrt {{{\left( { - 5} \right)}^2}} = - 5.\)

\(\sqrt {25} = 5.\)

\( - \sqrt 9 = - 3.\)

\(\sqrt {{x^2}} = \left| x \right|.\)

Nếu \(a \in \mathbb{Z}\) thì \(a \in \mathbb{R}.\)