(1)36x^2-1=0;
x^2=1/36
x=±1/6
(2)4x^2=81;
x^2=81/4
x=±9/2
(3)(x+5)^2=25
x+5=±5
x1=-10,x2=0
(4)x^2+2x+1=4.
（x+1)^2=4
x+1=±2
x1=-3,x2=1