Answer:
[tex]4 {x}^{2} + 2xy - 2 {y}^{2} [/tex]
Step-by-step explanation:
[tex](x + y)(x - 5y) + {3(x + y)}^{2} \\ x(x - 5y) + y(x - 5y) + 3(x + y)(x + y) \\ {x}^{2} - 5xy + xy - 5 {y}^{2} + (3x + 3y)(x + y) \\ {x}^{2} - 4xy - 5 {y}^{2} + 3x(x + y) + 3y(x + y) \\ {x}^{2} - 4xy - 5 {y}^{2} + 3 {x}^{2} + 3xy + 3xy + 3 {y}^{2} \\ {x}^{2} - 4xy - 5 {y}^{2} + 3 {x}^{2} + 6xy + 3 {y}^{2} \\ {x}^{2} + 3 {x}^{2} - 4xy + 6xy - 5 {y}^{2} + 3 {y}^{2} \\ 4 {x}^{2} + 2xy - 2 {y}^{2} [/tex]
