a)
[tex] {a}^{2} - {2}^{2} = {a}^{2} - 4[/tex]
b)
[tex] {x}^{2} - {1}^{2} = {x}^{2} - 1[/tex]
c)
[tex] {7}^{2} - {y}^{2} = 49 - {y}^{2} [/tex]
d)
[tex] {x }^{2} - {3}^{2} = {x}^{2} - 9[/tex]
e)
[tex] { \sqrt{3} }^{2} - { \frac{1}{ \sqrt{3} } }^{2} = 3 - \frac{1}{3} = \frac{2}{3} [/tex]