Question

Thực hiện tính: \(\sqrt{49}-5\sqrt{28}+\dfrac{1}{2}\sqrt{63}\)

Answer 1

\(=7-5\cdot2\sqrt{7}+\dfrac{1}{2}\cdot3\sqrt{7}=7-\dfrac{17}{2}\sqrt{7}\)

Answer 2

\(\sqrt{49}-5\sqrt{28}+\dfrac{1}{2}\sqrt{63}\)

\(=7-5\sqrt{7}\sqrt{4}+\dfrac{1}{2}\sqrt{7}\sqrt{9}\)

\(=7-10\sqrt{7}+\dfrac{3}{2}\sqrt{7}\)

\(=\sqrt{7}\left(\sqrt{7}-10+\dfrac{3}{2}\right)\)

\(=\sqrt{7}\left(\sqrt{7}-\dfrac{17}{2}\right)\)

\(=7-\dfrac{17}{2}\sqrt{7}\)