2) 4(x-5)-5x^2=5(1-x)(x+1)
4x-20-5x^2=5(1-x)(1+x)
4x-20-5x^2=5(1-x^2)
4x-20-5x^2=5-5x^2
4x-20=5
4x=5+20
4x=25
x=25:4
x=25/4

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

4х-20-5х^2=5(х+1^2)

4х-20-5х^2=5-5х^2

4х-20=5

4х=5+20

4х=25

х=25/4 или 6.25