1. x²+x<0
il scriem pe x²+x sub forma x(x+1).
x(x+1)<0. egalam ecuatia cu 0
x(x+1)=0
x=0
x+1=0⇒x=-1
facem tabel de semne
x |-inf -1 0 +inf
x |---------------------------0++++++++
x+1 |----------------0++++++++++++++
x(x+1)|+++++++++0---------0++++++++
solutia finala: x∈(-1;0)
2. x²≤9
x²-9≤0
(x-3)(x+3)≤0
x-3=0⇒x=3
x+3=0⇒x=-3
x |-inf -3 3 +inf
x-3 |-------------------------0+++++++++
x+3 |--------------0+++++++++++++++
(x-3)(x+3) |++++++++0----------0++++++++
solutia finala: x∈[-3; 3]
