10:{[10+10x(a-10)]÷10-10}=21-20÷2-10

Răspuns :

10:{[10+10a-100]÷10-10}=21-10-10
10:[(10a-90):10-10]=1
10:(a-9-10)=1
a-19=10
a=29

cel putin asa imi iese mie