Question Number 7809 by Tawakalitu. last updated on 16/Sep/16
$${x}\:+\:{y}\:+\:{z}\:=\:\mathrm{1}\:\:\:\:\:\:………\:\left({i}\right) \\ $$$${x}^{\mathrm{2}} \:+\:{y}^{\mathrm{2}} \:+\:{z}^{\mathrm{2}} \:=\:\mathrm{37}\:\:\:\:\:……..\:\left({ii}\right) \\ $$$${x}^{\mathrm{3}} \:+\:{y}^{\mathrm{2}} \:+\:{z}^{\mathrm{3}} \:=\:\mathrm{91}\:\:\:\:\:……..\:\left({iii}\right) \\ $$$$ \\ $$$${Solve}\:{simultaneously}.\: \\ $$
Commented by Tawakalitu. last updated on 16/Sep/16
$${That}\:{is}\:{the}\:{correct}\:{question}\:,\:{no}\:{mistake}\:{in}\:{the}\:{last} \\ $$$${equation}\:….{thanks}\:{for}\:{your}\:{help}. \\ $$
Commented by prakash jain last updated on 16/Sep/16
$${x}^{\mathrm{3}} +{z}^{\mathrm{3}} +{y}^{\mathrm{2}} =\mathrm{91} \\ $$$$\left({x}+{z}\right)\left({x}^{\mathrm{2}} +{z}^{\mathrm{2}} −{xz}\right)+{y}^{\mathrm{2}} =\mathrm{91} \\ $$$${from}\:\left({i}\right)\:{x}+{z}=\mathrm{1}−{y} \\ $$$${from}\:\left({ii}\right)\:{x}^{\mathrm{2}} +{z}^{\mathrm{2}} =\mathrm{37}−{y}^{\mathrm{2}} \\ $$$$\left(\mathrm{1}−{y}\right)\left(\mathrm{37}−{y}^{\mathrm{2}} −{xz}\right)+{y}^{\mathrm{2}} =\mathrm{91}\:\left({iv}\right) \\ $$$${from}\:\left({ii}\right) \\ $$$${x}^{\mathrm{2}} +{z}^{\mathrm{2}} +\mathrm{2}{xz}−\mathrm{2}{xz}+{y}^{\mathrm{2}} =\mathrm{37} \\ $$$$\left({x}+{z}\right)^{\mathrm{2}} −\mathrm{2}{xz}+{y}^{\mathrm{2}} =\mathrm{37} \\ $$$$\left(\mathrm{1}−{y}\right)^{\mathrm{2}} −\mathrm{2}{xz}+{y}^{\mathrm{2}} =\mathrm{37}\Rightarrow{xz}=\frac{\left(\mathrm{1}−{y}\right)^{\mathrm{2}} +{y}^{\mathrm{2}} −\mathrm{37}}{\mathrm{2}} \\ $$$${from}\:\left({iv}\right) \\ $$$$\left(\mathrm{1}−{y}\right)\left(\mathrm{37}−{y}^{\mathrm{2}} −\frac{\left(\mathrm{1}−{y}\right)^{\mathrm{2}} +{y}^{\mathrm{2}} −\mathrm{37}}{\mathrm{2}}\right)+{y}^{\mathrm{2}} =\mathrm{91} \\ $$$$\left(\mathrm{1}−{y}\right)\left(\frac{\mathrm{74}−\mathrm{2}{y}^{\mathrm{2}} −\mathrm{1}−{y}^{\mathrm{2}} +\mathrm{2}{y}−{y}^{\mathrm{2}} +\mathrm{37}}{\mathrm{2}}\right)+{y}^{\mathrm{2}} =\mathrm{91} \\ $$$$\left(\mathrm{1}−{y}\right)\left(\mathrm{110}+\mathrm{2}{y}\right)+\mathrm{2}{y}^{\mathrm{2}} =\mathrm{182} \\ $$$$\mathrm{110}−\mathrm{110}{y}+\mathrm{2}{y}−\mathrm{2}{y}^{\mathrm{2}} +\mathrm{2}{y}^{\mathrm{2}} =\mathrm{182} \\ $$$$\mathrm{110}−\mathrm{108}{y}=\mathrm{182} \\ $$$$\mathrm{55}−\mathrm{54}{y}=\mathrm{91} \\ $$$$−\mathrm{54}{y}=\mathrm{91}−\mathrm{55}=\mathrm{36}\Rightarrow{y}=−\frac{\mathrm{18}}{\mathrm{27}}=−\frac{\mathrm{2}}{\mathrm{3}} \\ $$
Commented by prakash jain last updated on 16/Sep/16
$${xz}={y}^{\mathrm{2}} −{y}−\mathrm{18}=\frac{\mathrm{4}}{\mathrm{9}}+\frac{\mathrm{2}}{\mathrm{3}}−\mathrm{18} \\ $$$${x}+{z}=\mathrm{1}−{y}=\frac{\mathrm{5}}{\mathrm{3}} \\ $$$${x}+{z}\:\mathrm{and}\:{xz}\:{are}\:{known}\:{so}\:{x}−{z}\:{can}\:{be}\:{found} \\ $$$${and}\:{value}\:{of}\:{x}\:{and}\:{z}\:{can}\:{be}\:{obtained}\:{as}\:{well}. \\ $$
Answered by Rasheed Soomro last updated on 18/Sep/16
$${x}\:+\:{y}\:+\:{z}\:=\:\mathrm{1}\:\:\:\:\:\:………\:\left({i}\right) \\ $$$${x}^{\mathrm{2}} \:+\:{y}^{\mathrm{2}} \:+\:{z}^{\mathrm{2}} \:=\:\mathrm{37}\:\:\:\:\:……..\:\left({ii}\right) \\ $$$${x}^{\mathrm{3}} \:+\:{y}^{\mathrm{2}} \:+\:{z}^{\mathrm{3}} \:=\:\mathrm{91}\:\:\:\:\:……..\:\left({iii}\right) \\ $$$$\left({i}\right)\Rightarrow{x}+{z}=\mathrm{1}−{y} \\ $$$$\left({ii}\right)\Rightarrow{x}^{\mathrm{2}} +{z}^{\mathrm{2}} =\mathrm{37}−{y}^{\mathrm{2}} \Rightarrow\left({x}+{z}\right)^{\mathrm{2}} −\mathrm{2}{xz}=\mathrm{37}−{y}^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\Rightarrow\left(\mathrm{1}−{y}\right)^{\mathrm{2}} −\mathrm{2}{xz}=\mathrm{37}−{y}^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\Rightarrow\left(\mathrm{1}−{y}\right)^{\mathrm{2}} +{y}^{\mathrm{2}} −\mathrm{37}=\mathrm{2}{xz} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\Rightarrow{xz}=\frac{\mathrm{1}−\mathrm{2}{y}+{y}^{\mathrm{2}} +{y}^{\mathrm{2}} −\mathrm{37}}{\mathrm{2}}=\frac{\mathrm{2}{y}^{\mathrm{2}} −\mathrm{2}{y}−\mathrm{36}}{\mathrm{2}}={y}^{\mathrm{2}} −{y}−\mathrm{18}…\left({iv}\right) \\ $$$$\left({iii}\right)\Rightarrow{x}^{\mathrm{3}} +{z}^{\mathrm{3}} =\mathrm{91}−{y}^{\mathrm{2}} \Rightarrow\left({x}+{z}\right)^{\mathrm{3}} −\mathrm{3}{xz}\left({x}+{z}\right)=\mathrm{91}−{y}^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\Rightarrow\left(\mathrm{1}−{y}\right)^{\mathrm{3}} −\mathrm{3}{xz}\left(\mathrm{1}−{y}\right)=\mathrm{91}−{y}^{\mathrm{2}} \\ $$$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\Rightarrow{xz}=\frac{\left(\mathrm{1}−{y}\right)^{\mathrm{3}} +{y}^{\mathrm{2}} −\mathrm{91}}{\mathrm{3}\left(\mathrm{1}−{y}\right)}…………………………….\left({v}\right) \\ $$$$\left({iv}\right),\left({v}\right)\Rightarrow{y}^{\mathrm{2}} −{y}−\mathrm{18}=\frac{\left(\mathrm{1}−{y}\right)^{\mathrm{3}} +{y}^{\mathrm{2}} −\mathrm{91}}{\mathrm{3}\left(\mathrm{1}−{y}\right)} \\ $$$${See}\:{the}\:{comments}\left({By}\:{prakash}\:{jain}\right)\:{for}\:{complete}\:{answer}. \\ $$