[tex] \sf \underline{ \red{Solution - }} \\ [/tex]
Given,
[tex] \sf{\quad { \dfrac{-7}{\sqrt{11} - \sqrt{5}} }} \\ [/tex]
The denominator is √11 - √5.
We know that
Rationalising factor of √a-√b is √a+√b.
Therefore, the rationalising factor of √11-√5 is √11+√5.
On rationalising the denominator them
[tex] \longrightarrow \sf{\quad { \dfrac{-7}{\sqrt{11} - \sqrt{5}} \times \dfrac{(\sqrt{11} + \sqrt{5})}{(\sqrt{11} + \sqrt{5})} }} \\ [/tex]
Multiplying (√11 + √5) with both the numerator of the fraction.
[tex] \longrightarrow \sf{\quad { \dfrac{-7(\sqrt{11} + \sqrt{5}) }{(\sqrt{11} - \sqrt{5})(\sqrt{11} + \sqrt{5})} }} \\ [/tex]
Performing multiplication in the numerator and by using identity (a + b)(a - b) = a² - b², solving further in the denominator.
[tex] \longrightarrow \sf{\quad { \dfrac{-7\sqrt{11} -7\sqrt{5}}{(\sqrt{11})^2 - (\sqrt{5})^2} }} \\ [/tex]
Writing the squares of the numbers in the denominator.
[tex] \longrightarrow \sf{\quad { \dfrac{-7\sqrt{11} -7\sqrt{5}}{11 -5} }} \\ [/tex]
Performing subtraction in the denominator.
[tex] \longrightarrow \quad \underline{ \boxed{ \dfrac{ \textbf{ \textsf{-7 }}\sqrt{ \textbf{ \textsf{11 }}} - \textbf{ \textsf{7}}\sqrt{ \textbf{ \textsf{5 }}}}{ \textbf{ \textsf{ 6}}}} } \\ [/tex]
Hence, the denominator is rationalised.
