[tex]a) {x}^{2} - 7x + 6 = 0[/tex]
[tex] {x}^{2} - 6x - x + 6 = 0[/tex]
[tex]x(x - 6) - (x - 6) = 0[/tex]
[tex](x - 6)(x - 1) = 0[/tex]
[tex]x - 6 = 0 = > x = 6 \: \in \: \mathbb{R}[/tex]
[tex]x - 1 = 0 = > x = 1 \: \in \: \mathbb{R}[/tex]
[tex]b) {x}^{2} - 8x - 20 = 0[/tex]
[tex] {x}^{2} - 10x + 2x - 20 = 0[/tex]
[tex]x(x - 10) + 2(x - 10) = 0[/tex]
[tex](x - 10)(x + 2) = 0[/tex]
[tex]x - 10 = 0 = > x = 10 \: \in \: \mathbb{R}[/tex]
[tex]x + 2 = 0 = > x = - 2 \: \in \: \mathbb{R}[/tex]
