Question

1, Rút gọn

A=\(3\sqrt{5a}-\sqrt{20a}+4\sqrt{45a}+\: \sqrt{a}\)

Với a\(\ge\)0

Answer 1

Với a\(\ge\)0,ta có

A=\(3\sqrt{5a}-\sqrt{20a}+4\sqrt{45a}+\sqrt{a}\)

A=\(3\sqrt{5a}-\sqrt{4.5a}+4\sqrt{9.5a}+\sqrt{a}\)

A=\(3\sqrt{5a}-2\sqrt{5a}+12\sqrt{5a}+\sqrt{a}\)

A=\(13\sqrt{5a}+\sqrt{a}\)

Answer 2

Lời giải:

\(A=3\sqrt{5a}-\sqrt{20a}+4\sqrt{45a}+\sqrt{a}=3\sqrt{5}.\sqrt{a}-\sqrt{4}.\sqrt{5}.\sqrt{a}+4.\sqrt{9}.\sqrt{5}.\sqrt{a}+\sqrt{a}\)

\(=3\sqrt{5}.\sqrt{a}-2\sqrt{5}\sqrt{a}+12\sqrt{5}.\sqrt{a}+\sqrt{a}\)

\(=\sqrt{a}(3\sqrt{5}-2\sqrt{5}+12\sqrt{5}+1)=\sqrt{a}(13\sqrt{5}+1)\)