\(\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}{h}\)
\(\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x}}-\sqrt{\frac{1}{x+h}}}{h}\)
\(\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x-h}}+\sqrt{\frac{1}{x}}}{h}\)
\(={\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}{h} \cdot \frac{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}{h} \cdot \frac{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}}}{h} \cdot \frac{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{1}{x+h}+\frac{1}{x}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{1}{x+h}-\frac{1}{x}}{h\left ( \sqrt{\frac{1}{x+h}}-\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{1}{x+h}-\frac{1}{x}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{x-(x+h)}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{\frac{h}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{x-(x+h)}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{\frac{-h}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{\frac{x+(x+h)}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{\frac{2x+h}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{-h\frac{1}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{\cancel{-h}\frac{1}{x(x+h)}}{\cancel{h}\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{-h\frac{1}{x(x+h)}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{-\cancel{h}\frac{1}{x(x+h)}}{\cancel{h}\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(={\displaystyle\lim_{h \to 0}\frac{-h\frac{1}{x+h}}{h\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\\={\displaystyle\lim_{h \to 0}\frac{-\cancel{h}\frac{1}{x+h}}{\cancel{h}\left ( \sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}} \right )}}=\)
\(=\displaystyle\lim_{h \to 0}\frac{-\frac{1}{x(x+h)}}{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}=\\=\displaystyle\lim_{h \to 0}\frac{-1}{(x^{2}+xh)\Big (\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}\Big)}=\\=\displaystyle\lim_{h \to 0}\frac{-1}{(x^{2}+\cancelto{0}{xh})\Big (\sqrt{\frac{1}{x+\cancelto{0}{h}}}+\sqrt{\frac{1}{x}}\Big)}=\\=-\displaystyle\frac{1}{2x^{2}\sqrt{\frac{1}{x}}}\)
\(=\displaystyle\lim_{h \to 0}\frac{\frac{1}{x(x+h)}}{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}=\\=\displaystyle\lim_{h \to 0}\frac{1}{(x^{2}+xh)\Big (\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}\Big)}=\\=\displaystyle\lim_{h \to 0}\frac{1}{(x^{2}+\cancelto{0}{xh})\Big (\sqrt{\frac{1}{x+\cancelto{0}{h}}}+\sqrt{\frac{1}{x}}\Big)}=\\=\displaystyle\frac{1}{2x^{2}\sqrt{\frac{1}{x}}}\)
\(=\displaystyle\lim_{h \to 0}\frac{-\frac{1}{x(x+h)}}{\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}}=\\=\displaystyle\lim_{h \to 0}\frac{-1}{(x^{2}+xh)\Big (\sqrt{\frac{1}{x+h}}+\sqrt{\frac{1}{x}}\Big)}=\\=\displaystyle\lim_{h \to 0}\frac{-1}{(x^{2}+\cancelto{x}{xh})\Big (\sqrt{\frac{1}{x+\cancelto{0}{h}}}+\sqrt{\frac{1}{x}}\Big)}=\\=-\displaystyle\frac{1}{2(x^{2}+x)\sqrt{\frac{1}{x}}}\)
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