equation of st. line & circle

Actually, your work is in the right direction, but you made a mistake in the last part.

√[5(√5-5)^2]=√5*√[(√5-5)^2]=√5*-(√5-5)=-5(1-√5)=5(√5-1)

Note that for x<0, √(x^2)=│x│=-x