1) (x-5) ^2 + (x+4) ^2=2x^2

2) 5x^2-12x+7=0

3) x^2-121=0

4) 5x^2+20x=0

5) (x-2) (-x-1) = 0

1) x^2-10x+25+x^2+8x+16=2x^2

2x = 41

x = 20,5

2) 5x^2-12x+7=0

D = 144 - 140 = 4

x1,2 = (12+-2) / 10

x1 = 1,4 x2 = 1

3) x^2-121=0

x^2=121

x1 = 11

x2 = - 11

4) 5x^2+20x=0

5x (x+4) = 0

x=0 или x = 4

5) (x-2) (-x-1) = 0

x=2 или x = - 1

вроде так