0\\\\5ab\sqrt{-\frac{a^7}{5b}}=-\sqrt{-\frac{5^2a^2b^2\cdot a^7}{5b}} =-\sqrt{-\frac{5a^2b\cdot a^7}{1}}=-\sqrt{-5a^9\cdot b}" alt="a\leq 0\; \; ,\; \; b>0\\\\5ab\sqrt{-\frac{a^7}{5b}}=-\sqrt{-\frac{5^2a^2b^2\cdot a^7}{5b}} =-\sqrt{-\frac{5a^2b\cdot a^7}{1}}=-\sqrt{-5a^9\cdot b}" align="absmiddle" class="latex-formula">