A(a-2)-a^2> 5-3a 3x(3x-1)-9x^2< 3x+6 5y^2-y(y+4)≧100 7c(c-2)-c(7c+1)< 3

A(a-2)-a^2>5-3a
a^2-2a-a^2>5-3a
-2a+3a>5
a>5

3x(3x-1)-9x^2<3x+6
9x^2-3x-9x^2-3x<6
-6x<6
x>-1

5y^2-y(y+4)≥100
5y^2-y^2-4y≥100
4y^2-4y-100≥0
y^2-y-25≥0

7c(c-2)-c(7c+1)<3
7c^2-14c-7c^2-c<3
-15c<3
-c<3/15
c>-1/5