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lim-x-0-1-1-1-x-1-1-1-x-x-




Question Number 171079 by greougoury555 last updated on 07/Jun/22
      lim_(x→0)  (((√(1+(√(1+(√(1−x))))))−(√(1+(√(1+(√(1+x)))))))/x)=?
$$\:\:\:\:\:\:\underset{{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\:\frac{\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+\sqrt{\mathrm{1}−{x}}}}−\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+{x}}}}}{{x}}=? \\ $$
Commented by benhamimed last updated on 07/Jun/22
((−1)/(24))
$$\frac{−\mathrm{1}}{\mathrm{24}} \\ $$
Commented by greougoury555 last updated on 08/Jun/22
Answered by qaz last updated on 07/Jun/22
lim_(x→0) (((√(1+(√(1+(√(1−x))))))−(√(1+(√(1+(√(1+x)))))))/x)  =lim_(x→0) (1/x)((√(1+(√(2−(1/2)x+o(x)))))−(√(1+(√(2+(1/2)x+o(x))))))  =lim_(x→0) (1/x)((√(1+(√2)(1−(1/8)x+o(x))))−(√(1+(√2)(1+(1/8)x+o(x)))))  =lim_(x→0) ((√(1+(√2)))/x)((√(1−((√2)/(8(1+(√2))))x+o(x)))−(√(1+((√2)/(8(1+(√2))))x+o(x))))  =lim_(x→0) ((√(1+(√2)))/x)(−((√2)/(8(1+(√2))))x+o(x))  =−(1/8)(√(2/(1+(√2))))
$$\underset{\mathrm{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\frac{\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+\sqrt{\mathrm{1}−\mathrm{x}}}}−\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+\sqrt{\mathrm{1}+\mathrm{x}}}}}{\mathrm{x}} \\ $$$$=\underset{\mathrm{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\frac{\mathrm{1}}{\mathrm{x}}\left(\sqrt{\mathrm{1}+\sqrt{\mathrm{2}−\frac{\mathrm{1}}{\mathrm{2}}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)}}−\sqrt{\mathrm{1}+\sqrt{\mathrm{2}+\frac{\mathrm{1}}{\mathrm{2}}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)}}\right) \\ $$$$=\underset{\mathrm{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\frac{\mathrm{1}}{\mathrm{x}}\left(\sqrt{\mathrm{1}+\sqrt{\mathrm{2}}\left(\mathrm{1}−\frac{\mathrm{1}}{\mathrm{8}}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)\right)}−\sqrt{\mathrm{1}+\sqrt{\mathrm{2}}\left(\mathrm{1}+\frac{\mathrm{1}}{\mathrm{8}}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)\right)}\right) \\ $$$$=\underset{\mathrm{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\frac{\sqrt{\mathrm{1}+\sqrt{\mathrm{2}}}}{\mathrm{x}}\left(\sqrt{\mathrm{1}−\frac{\sqrt{\mathrm{2}}}{\mathrm{8}\left(\mathrm{1}+\sqrt{\mathrm{2}}\right)}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)}−\sqrt{\mathrm{1}+\frac{\sqrt{\mathrm{2}}}{\mathrm{8}\left(\mathrm{1}+\sqrt{\mathrm{2}}\right)}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)}\right) \\ $$$$=\underset{\mathrm{x}\rightarrow\mathrm{0}} {\mathrm{lim}}\frac{\sqrt{\mathrm{1}+\sqrt{\mathrm{2}}}}{\mathrm{x}}\left(−\frac{\sqrt{\mathrm{2}}}{\mathrm{8}\left(\mathrm{1}+\sqrt{\mathrm{2}}\right)}\mathrm{x}+\mathrm{o}\left(\mathrm{x}\right)\right) \\ $$$$=−\frac{\mathrm{1}}{\mathrm{8}}\sqrt{\frac{\mathrm{2}}{\mathrm{1}+\sqrt{\mathrm{2}}}} \\ $$

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