Toán Lớp 9: Chứng minh rằng
Căn(21+8 căn5)/4 + căn5 x căn(9-4 căn5) =căn5 -2
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 9: Chứng minh rằng
Căn(21+8 căn5)/4 + căn5 x căn(9-4 căn5) =căn5 -2
Comments ( 1 )
\dfrac{{\sqrt {21 + 8\sqrt 5 } }}{{4 + \sqrt 5 }}.\sqrt {9 – 4\sqrt 5 } \\
= \dfrac{{\sqrt {16 + 5 + 2.4\sqrt 5 } }}{{4 + \sqrt 5 }}.\sqrt {5 + 4 – 2.2\sqrt 5 } \\
= \dfrac{{\sqrt {{{\left( {4 + \sqrt 5 } \right)}^2}} }}{{4 + \sqrt 5 }}.\sqrt {{{\left( {\sqrt 5 – 2} \right)}^2}} \\
= \dfrac{{4 + \sqrt 5 }}{{4 + \sqrt 5 }}.\left| {\sqrt 5 – 2} \right| = \sqrt 5 – 2
\end{array}$