\(a^3+b^3+3\left(a^2+b^2\right)+4\left(a+b\right)+4=0\)
<=> \(\left(a+1\right)^3+\left(b+1\right)^3+\left(a+1\right)+\left(b+1\right)=0\)
<=> \(\left(a+1+b+1\right)\left[\left(a+1\right)^2+\left(b+1\right)^2-\left(a+1\right)\left(b+1\right)+1\right]=0\)
<=> \(a+b+2=0\)
<=> a + b = - 2
Khi đó: 2020 (a +b ) = 2020. ( -2) = -4040