Write the equation of the family of lines with slope -1/2 and find the two members of the family 5 units away from the origin.

Answer 1

Let our two lines be y = -1/2 x ± k
The line y=2x is perpendicular to the given family of lines.
Suppose y=2x meets y = -1/2 x + k at (a,b).
Since b=2a, and a^2+b^2=25, find the intersection of the lines (solve for k) and now your lines are identified.