Объяснение:

1)

а=1; b=7; c= -18

[tex]x = \frac{ - 7 + \sqrt{7 {}^{2} - 4 \times 1 \times ( - 18) } }{2 \times 1} [/tex]

[tex]x = \frac{ - 7 + \sqrt{121} }{2} [/tex]

[tex]x = \frac{ - 7 + 11}{2} [/tex]

[tex]x = \frac{ - 7 - \\ 11}{2} [/tex]

х=2;

х=-9

2)

а= 1; b=-1; c= -42

[tex]x = \frac{ - ( - 1) + \sqrt{( - 1) {}^{2} - 4 \times 1 \times ( - 42) } }{2 \times 1} [/tex]

[tex]x = \frac{1 + \sqrt{1 + 168} }{2} [/tex]

[tex]x = \frac{ 1 + \sqrt{169} }{2} [/tex]

[tex]x = \frac{1 + 13}{2} [/tex]

[tex]x = \frac{1 + 13}{2} [/tex]

[tex]x = \frac{1 - 13}{2} [/tex]

х=7

х= -6