va rog frumos repede ajutati-ma

[tex]7a ^{4} b + 7a ^{3} b ^{2} - {a}^{4} b + 2 {a}^{3} {b}^{2} [/tex]
[tex] = 6 {a}^{4} b + 9 {a}^{3} b ^{2} [/tex]