Question Number 98598 by MWSuSon last updated on 15/Jun/20
$$\boldsymbol{{let}}\:\boldsymbol{{A}}=\left(\mathrm{3},\mathrm{4}\right)\:\boldsymbol{{and}}\:\boldsymbol{{B}}\:\boldsymbol{{is}}\:\boldsymbol{{a}}\:\boldsymbol{{variable}}\:\boldsymbol{{point}} \\ $$$$\boldsymbol{{on}}\:\boldsymbol{{the}}\:\boldsymbol{{line}}\:\mid\boldsymbol{{x}}\mid=\mathrm{6}.\:\boldsymbol{{if}}\:\overline {\boldsymbol{{AB}}}<\mathrm{4},\:\boldsymbol{{then}}\:\boldsymbol{{the}} \\ $$$$\boldsymbol{{number}}\:\boldsymbol{{of}}\:\boldsymbol{{position}}\:\boldsymbol{{of}}\:\boldsymbol{{B}}\:\boldsymbol{{with}}\:\boldsymbol{{integral}} \\ $$$$\boldsymbol{{coordinates}}\:\boldsymbol{{is}}? \\ $$$$\boldsymbol{{please}}\:\boldsymbol{{help}}! \\ $$
Commented by bobhans last updated on 15/Jun/20
$$\mid{x}\mid\:=\:\mathrm{6}\:\Rightarrow\begin{cases}{{x}\:=\:−\mathrm{6}\:{or}}\\{{x}=\:\mathrm{6}}\end{cases} \\ $$$$\mathrm{case}\:\left(\mathrm{1}\right)\:\mathrm{let}\:\mathrm{B}\left(−\mathrm{6},\mathrm{y}\right)\:\mathrm{then}\:\sqrt{\left(\mathrm{y}−\mathrm{4}\right)^{\mathrm{2}} +\mathrm{81}}\:<\:\mathrm{4} \\ $$$$\left(\mathrm{y}−\mathrm{4}\right)^{\mathrm{2}} +\mathrm{81}\:<\:\mathrm{16}\:\Rightarrow\mathrm{y}\:=\:\varnothing \\ $$$$\mathrm{case}\left(\mathrm{2}\right)\:\mathrm{let}\:\mathrm{B}\left(\mathrm{6},\mathrm{y}\right)\:\mathrm{then}\:\sqrt{\left(\mathrm{y}−\mathrm{4}\right)^{\mathrm{2}} +\mathrm{9}}\:<\:\mathrm{4} \\ $$$$\left(\mathrm{y}−\mathrm{4}\right)^{\mathrm{2}} −\mathrm{7}\:<\mathrm{0}\:\Rightarrow\left(\mathrm{y}−\mathrm{4}−\sqrt{\mathrm{7}}\right)\left(\mathrm{y}−\mathrm{4}+\sqrt{\mathrm{7}}\right)\:<\:\mathrm{0} \\ $$$$\mathrm{4}\:−\:\sqrt{\mathrm{7}}\:<\:\mathrm{y}\:<\:\mathrm{4}+\sqrt{\mathrm{7}}\: \\ $$$$\mathrm{1}.\mathrm{354}\:<\:\mathrm{y}\:<\:\mathrm{6}.\mathrm{64} \\ $$$$\mathrm{so}\:\mathrm{position}\:\mathrm{of}\:\mathrm{B}\:\mathrm{with}\:\mathrm{integral}\:\mathrm{coordinates} \\ $$$$\mathrm{where}\:\mathrm{y}\:\in\left\{\mathrm{2},\mathrm{3},\mathrm{4},\mathrm{5},\mathrm{6}\right\} \\ $$
Commented by MWSuSon last updated on 15/Jun/20
Thanks a lot.