Question Number 161065 by cortano last updated on 11/Dec/21
$$\:\begin{cases}{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:+\sqrt[{\mathrm{8}}]{{x}−{abc}}\:=\:{a}}\\{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:−\sqrt[{\mathrm{8}}]{{x}−{abc}}\:=\:{b}}\\{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:−\sqrt[{\mathrm{4}}]{{x}−{abc}}\:=\:{c}}\end{cases} \\ $$$$\:{find}\:\sqrt{{x}+{abc}}\:+\sqrt{{x}−{abc}} \\ $$
Answered by Rasheed.Sindhi last updated on 12/Dec/21
$$\:\begin{cases}{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:+\sqrt[{\mathrm{8}}]{{x}−{abc}}\:=\:{a}….\left({i}\right)}\\{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:−\sqrt[{\mathrm{8}}]{{x}−{abc}}\:=\:{b}…..\left({ii}\right)}\\{\sqrt[{\mathrm{4}}]{{x}+{abc}}\:−\sqrt[{\mathrm{4}}]{{x}−{abc}}\:=\:{c}…..\left({iii}\right)}\end{cases} \\ $$$$\mathrm{2}\sqrt[{\mathrm{4}}]{{x}+{abc}}\:={a}+{b} \\ $$$$\sqrt[{\mathrm{4}}]{{x}+{abc}}\:=\frac{{a}+{b}}{\mathrm{2}} \\ $$$$\left(\sqrt[{\mathrm{4}}]{{x}+{abc}}\:\right)^{\mathrm{2}} =\left(\frac{{a}+{b}}{\mathrm{2}}\right)^{\mathrm{2}} \\ $$$$\sqrt{{x}+{abc}}\:=\left(\frac{{a}+{b}}{\mathrm{2}}\right)^{\mathrm{2}} ………..{A} \\ $$$$\mathrm{2}\sqrt[{\mathrm{8}}]{{x}−{abc}}\:={a}−{b} \\ $$$$\sqrt[{\mathrm{8}}]{{x}−{abc}}\:=\frac{{a}−{b}}{\mathrm{2}} \\ $$$$\left(\sqrt[{\mathrm{8}}]{{x}−{abc}}\:\right)^{\mathrm{4}} =\left(\frac{{a}−{b}}{\mathrm{2}}\right)^{\mathrm{4}} \\ $$$$\sqrt{{x}−{abc}}\:=\left(\frac{{a}−{b}}{\mathrm{2}}\right)^{\mathrm{4}} ………{B} \\ $$$${A}+{B}:\:\sqrt{{x}+{abc}}\:+\sqrt{{x}−{abc}}\: \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:=\left(\frac{{a}+{b}}{\mathrm{2}}\right)^{\mathrm{2}} +\left(\frac{{a}−{b}}{\mathrm{2}}\right)^{\mathrm{4}} \\ $$$${Without}\:{using}\:\left({iii}\right)\:!!! \\ $$