$\frac{ 72081 }{ 50 }-\sqrt{ {8.7}^{2}-13.26 }$
Convert the decimal into a fraction$\frac{ 72081 }{ 50 }-\sqrt{ {\left( \frac{ 87 }{ 10 } \right)}^{2}-13.26 }$
Convert the decimal into a fraction$\frac{ 72081 }{ 50 }-\sqrt{ {\left( \frac{ 87 }{ 10 } \right)}^{2}-\frac{ 663 }{ 50 } }$
To raise a fraction to a power, raise the numerator and denominator to that power$\frac{ 72081 }{ 50 }-\sqrt{ \frac{ 7569 }{ 100 }-\frac{ 663 }{ 50 } }$
Subtract the fractions$\frac{ 72081 }{ 50 }-\sqrt{ \frac{ 6243 }{ 100 } }$
To take a root of a fraction, take the root of the numerator and denominator separately$\begin{align*}&\frac{ 72081 }{ 50 }-\frac{ \sqrt{ 6243 } }{ 10 } \\&\approx1433.71873\end{align*}$