Verified answer

1) (5x+2)^2+(x-10)^2=208

(25x^2+20x+4)+(x^2-20x+100)-208=0

26x^2=104

x^2=4

x1=2

x2=-2

2) (2x+1)^2-(2x-1)^2=218

    (4x^2+4x+1)-(4x^2-4x+1)-218=0

     8x=218

     x=27,25

3) 25x^2-30x+9=16

   25x^2-30x-7=0

D=1600

x1=-0,2

x2=1,4