Question

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

Answer 1

`=(5\sqrt3)^2-(3\sqrt5)^2 = 75 - 45=30`

Answer 2

\(\left(5\sqrt{3}-3\sqrt{5}\right)\left(5\sqrt{3}+3\sqrt{5}\right)=\left(5\sqrt{3}\right)^2-\left(3\sqrt{5}\right)^2\)

\(=25.3-9.5=75-45=30\)

Answer 3

Áp dụng hđt đáng nhớ \(\left(a-b\right)\left(a+b\right)=a^2-b^2\) ta có:

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

\(=\left(5\sqrt{3}\right)^2-\left(3\sqrt{5}\right)^2\)

\(=25.3-9.5\)

\(=75-45\)

\(=30\)