Question

4. Trục căn thức ở mẫu :
a. 10/(sqrt(5))
b. 9/(2sqrt(3))
c. (sqrt(2) - 2)/(1 - sqrt(2))
d. 1/(sqrt(3) + 2)
e. 7/(3sqrt(2) - 5)
 

Answer 1

\(\dfrac{10}{\sqrt{5}}=\dfrac{10.\sqrt{5}}{\sqrt{5}.\sqrt{5}}=\dfrac{10\sqrt{5}}{5}=2\sqrt{5}\)

\(\dfrac{9}{2\sqrt{3}}=\dfrac{9\sqrt{3}}{2\sqrt{3}.\sqrt{3}}=\dfrac{9\sqrt{3}}{2.3}=\dfrac{3\sqrt{3}}{2}\)

\(\dfrac{\sqrt{2}-2}{1-\sqrt{2}}=\dfrac{\sqrt{2}\left(1-\sqrt{2}\right)}{1-\sqrt{2}}=\sqrt{2}\)

\(\dfrac{1}{\sqrt{3}+2}=\dfrac{2-\sqrt{3}}{\left(2-\sqrt{3}\right)\left(2+\sqrt{3}\right)}=\dfrac{2-\sqrt{3}}{2^2-3}=2-\sqrt{3}\)

\(\dfrac{7}{3\sqrt{2}-5}=\dfrac{7\left(3\sqrt{2}+5\right)}{\left(3\sqrt{2}-5\right)\left(3\sqrt{2}+5\right)}=\dfrac{7\left(3\sqrt{2}+5\right)}{\left(3\sqrt{2}\right)^2-5^2}=\dfrac{7\left(3\sqrt{2}+5\right)}{-7}=-3\sqrt{2}-5\)