Question

Thực hiện phép tính , rút gọn biểu thức sau

\(\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)\)

\(\left(\sqrt{45}+\sqrt{63}\right)\left(\sqrt{7}-\sqrt{5}\right)\)

Answer 1

\(\left(\sqrt{5}+\sqrt{3}\right)\left(5-\sqrt{15}\right)\)

\(\Rightarrow5\sqrt{5}-\sqrt{75}+5\sqrt{3}-\sqrt{45}\)

\(\Rightarrow5\sqrt{5}-5\sqrt{3}+5\sqrt{3}-\sqrt{45}\)

\(\Rightarrow5\sqrt{5}-3\sqrt{5}\)

\(\Rightarrow2\sqrt{5}\)

\(\left(\sqrt{45}+\sqrt{63}\right)\left(\sqrt{7}-\sqrt{5}\right)\)

\(\Rightarrow\left(3\sqrt{5}+3\sqrt{7}\right)\left(\sqrt{7}-\sqrt{5}\right)\)

\(\Rightarrow3\sqrt{35}-15+21-3\sqrt{35}\)

\(\Rightarrow6\)

Answer 2

=( √5+√3)* √5*(√5 -√3)

=√5 *2

=2√5

Answer 3

=3*(√7+√5)*( √7-√5)

=6