determinant-x-7-9-8-x-determinant-7-0-3-5-x-6-3-5-x-9-

Question Number 90316 by M±th+et£s last updated on 22/Apr/20

| \begin{matrix} x & 7 \\ 9 & 8 - x \end{matrix} | = | \begin{matrix} 7 & 0 & - 3 \\ - 5 & x & - 6 \\ - 3 & - 5 & x - 9 \end{matrix} |

Commented by john santu last updated on 23/Apr/20

8 x - x^{2} - 63 = 7 (x^{2} - 9 x - 30) -

3 (25 + 3 x)

- x^{2} + 8 x - 63 = 7 x^{2} - 63 x - 210 - 75 - 9 x

- x^{2} + 8 x - 63 = 7 x^{2} - 72 x - 285

8 x^{2} - 80 x - 222 = 0

4 x^{2} - 40 x - 111 = 0

x = \frac{40 \pm \sqrt{40^{2} + 444}}{8}

Commented by M±th+et£s last updated on 23/Apr/20

s i r i t h i n k i t s 8 x^{2} - 80 x - 222 a n d

t h a n k y o u n o w i c a n d o i t w i t h m y s e l f

Answered by M±th+et£s last updated on 23/Apr/20

Commented by john santu last updated on 23/Apr/20

y e s . g o o d