Question 179973
Use the distance formula,
{{{D=sqrt((x[1]-x[2])^2+(y[1]-y[2])^2)}}}
{{{15^2=(1-x[2])^2+(0-10)^2}}}
{{{225=(1-x[2])^2+100}}}
{{{(1-x[2])^2=125}}}
{{{(1-x[2])=0 +- sqrt(125)}}}
{{{x[2]=1 +- 5*sqrt(5)}}}
or approximately,
{{{x[2]=1 +- 11.2}}}
{{{x[2]=12.2}}} and
{{{x[2]=-10.2}}}
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The green line is y=10.
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{{{drawing( 300, 300, -15, 15, -15, 15,grid( 1 ),
circle( 1,0, .6 ),
circle( 12.2,10, .4 ),
circle(-10.2,10,.4),
line(1,0,12.2,10),
line(1,0,-10.2,10),
green(line( -20, 10, 20, 10)))}}}
The two points that are 15 units from (1,0) and lie on y=10 are (12.2,10) and (-10.2,10).