Ayudenme porfavor que no entiendo

Respuesta:
Completar los espacios requeridos !
a)
[tex](a + b) ^{2} = [/tex]
[tex] = {a}^{2} + 2ab + {b}^{2} [/tex]
b)
[tex] {(x - y)}^{2} = [/tex]
[tex] = {x}^{2} - 2xy + {y}^{2} [/tex]
C)
[tex] {(2a + 3b)}^{2} = [/tex]
[tex] = 4 {a}^{2} + 12ab + 9 {b}^{2} [/tex]
D)
[tex] {(5 {m}^{2} + 4n) }^{2} = [/tex]
[tex] = 25 {m}^{4} + 40 {m}^{2} n + 16 {n}^{2} [/tex]
Saludos