0\ \ ,\ \ \dfrac{261\, \sqrt[18]{r}\cdot \sqrt[27]{r}}{3\, \sqrt[54]{r^5}}=\dfrac{261\cdot r^{\frac{1}{18}+\frac{1}{27}}}{3\cdot r^{\frac{5}{54}}}=\dfrac{87\cdot r^{\frac{5}{54}}}{r^{\frac{5}{54}}}=87" alt="r>0\ \ ,\ \ \dfrac{261\, \sqrt[18]{r}\cdot \sqrt[27]{r}}{3\, \sqrt[54]{r^5}}=\dfrac{261\cdot r^{\frac{1}{18}+\frac{1}{27}}}{3\cdot r^{\frac{5}{54}}}=\dfrac{87\cdot r^{\frac{5}{54}}}{r^{\frac{5}{54}}}=87" align="absmiddle" class="latex-formula">