Ответ:

a)

[tex]{x}^{2} - 0.64 = 0[/tex]

[tex] {x}^{2} = 0.64[/tex]

x=±0.8

б)

[tex]81 - 49 {y}^{2} = 0[/tex]

[tex]49 {y}^{2} = 81[/tex]

[tex] {y}^{2} = \frac{81}{49} [/tex]

[tex]y = + - \frac{9}{7} [/tex]