Question

6. Розв'яжіть рівняння

Answer 1

$\displaystyle\bf\\\frac{x^{2}-x-72 }{9x+72} =0\\\\\\\left \{ {{x^{2} -x-72=0} \atop {9x+72\neq 0}} \right.\\\\\\\left \{ {{x^{2} -x-72=0} \atop {9x\neq -72}} \right. \\\\\\\left \{ {{x^{2} -x-72=0} \atop {x\neq -8}} \right.\\\\\\x^{2} -x-72=0\\\\D=(-1)^{2} -4\cdot(-72)=1+288=289=17^{2} \\\\\\x_{1} =\frac{1+17}{2} =\frac{18}{2} =9\\\\\\x_{2} =\frac{1-17}{2} =\frac{-16}{2} =-8 \ - \ ne \ podxodit\\\\\\Otvet \ : \ B) \ \ 9$

Answer 2

$\frac{ {x}^{2} - x - 72 }{9x + 72} = 0 \\ x\neq - 8 \\ {x {}^{2} - x - 72}^{} = 0$

По теореме Виета:

${x}^{2} + bx + c = 0\\ x_{1} + x_{2} = - b\\ x_{1} x_{2} = c$

$x_{1} + x_{2} = 1 \\ x_{1} x_{2} = - 72 \\ x_{1} = 9 \\ x_{2} = - 8$

Второй корень не подходит

Ответ: В) 9