# How do you ddd: 3a^3+8a-6 and 4a^2-9a+11?

You must add together terms that have the same kind of variables (such as ${a}^{3}$) according to their numerical values (with sign):
You can add: $5 {a}^{3} + 2 {a}^{3} = 7 {a}^{3}$ the variables are of the same kind ${a}^{3}$ so you simply add the mumerical values;
You cannot add: $5 {a}^{3} + 3 {a}^{2}$ the variables are different!!!!
If you add correctly, you should get $3 {a}^{3} + 4 {a}^{2} - a + 5$.