a) x^2 - 4x -20 + 5x = 0

 x^2 +x - 20= 0

D = 1 +80 = 81 = 9^2

x1= (-1 - 9) /2

x1 = -5

x2= (-1+9)/2

x2 = 4

2) b^2 -b +1 - b= 0

b^2 - 2b +1 =0

d = 4 - 4 = 0

d1 = 2/2 = 1

3) 2p - 4 +2p - p^2

-p^2 +4p - 4=0

p^2 -4p +4=0

D= 16- 16= 0

P1= 4/2 = 2

а)x(x-4)-5(4-x)=x(x-4)+5(x-4)=(x-4)(x+5)

b)b(b-1)+(1-b)=b(b-1)-(b-1)=(b-1)(b-1)=(b-1)^2

v)2(p-2)+p(2-p) =-2(2-p)+p(2-p)=(2-p)(p-2)=-(2-p)(2+p)=-(4-p^2)=p^2-4