Question 335171
Use the distance formula,
{{{D^2=(x1-x2)^2+(y1-y2)^2}}}
{{{D^2=(x-1)^2+(-2-5)^2}}}
{{{D^2=(x-1)^2+(-7)^2}}}
{{{D^2=(x-1)^2+49}}}
{{{(x-1)^2=D^2-49}}}
{{{x-1=0 +- sqrt(D^2-49)}}}
{{{highlight(x=1 +- sqrt(D^2-49))}}}