解：?$(1)x-5=±4$?
?$x_1=9 $?，?$x_2=1$?
?$(2)x^2-2x+1=4+1$?
?$(x-1)^2=5$?
?$x-1=±\sqrt 5$?
?$x_1=1+\sqrt 5 $?，?$x_2=1-\sqrt 5$?
?$(3)(y-1)^2-2y(y-1)=0$?
?$(y-1)(y-1-2y)=0$?
?$y_{1}=1$?，?$y_{2}=-1$?
?$(4)a=2$?，?$b=-7$?，?$c=1$?
?$△=(-7)^2-4×2×1=41＞0$?
∴?$x=\frac {7±\sqrt {41}}{2×2}$?
?$x_1=\frac {7+\sqrt {41}}4 $?，?$x_2=\frac {7-\sqrt {41}}4$?
