x-5≥2x

seven

h & gt 160

eight

9-3x >0

3x< Nine

X< three

Non-negative integer solution: 0, 1, 2

nine

a^3-a=a(a^2- 1)=a(a+ 1)(a- 1)

10

20 12^2-20 1 1*20 12=20 12(20 12-20 1 1)=20 12* 1=20 12

1 1

a^2-b^2=(a+b)(a-b)=5* 1=5

12

-x^4-3x^2+x=-x(x^3+3x- 1)

x^3+3x- 1

13

1 & lt； 2x+ 1 & lt； three

0 & lt2x & lt2

0 & ltx & lt 1