1) x²+16x+64=0

(x+8)²=0

x+8=0

x=-8

2) 36x²-12x+1=0

(6x-1)²=0

6x-1=0

6x=1

x=1/6

3) 4x²+9=-12x

4x²+9-12x=0

4x²-12x+9=0

(2x-3)²=0

2x=3

x=3/2

4) x²=0.4x-0.04

25x²=10x-1

(5x-1)²=0

5x-1=0

5x=1

x=1/5