Question

алгебра 8 класс,помогите пожалуйста

Answer 1

Ответ:

№1

${x}^{2} - 9x + 14 = 0 \\ a = 1 \: b = - 9 \: c = 14\\ D = {b}^{2} - 4ac = ( - 9 {)}^{2} - 4 \times 1 \times 14 = 81 - 56 = 25 \\ \sqrt{25} = 5 \\ х½ = \frac{ - b± \sqrt{D} }{2a} = \frac{9±5}{2} = 7 ;2 \\ (x - 7)(x - 2) = 0$

Ответ а

№2

$\frac{x + 3}{ {x}^{2} - 2x - 15 }$

${x}^{2} - 2x - 15 \\ a = 1 \: \: b = - 2 \: c = - 15 \\ D = ( - 2 {)}^{2} - 4 \times 1 \times ( -15) = 4 + 60 = 64 \\ \sqrt{64} = 8 \\ х½ = \frac{2±8}{2} = 5 ; - 3 \\ (x - 5)(x + 3)$

$\frac{x + 3}{(x - 5)(x + 3)} =$

Сократим х+3 и х+3:

$= \frac{1}{x - 5}$

Ответ г

№3

$2(x - 10)(x + 3) = 0 \\ 2( {x}^{2} + 3x - 10x - 30) = 0 \\ 2 ( {x}^{2} - 7x - 30) = 0 \\ 2 {x}^{2} - 14x - 60 = 0 \\ a = 2 \: b = - 14 \: c = - 60 \\ D = ( - 14 {)}^{2} - 4 \times 2 \times ( - 60) = 196 + 480 = 676 \\ \sqrt{676} = 26 \\ х½ = \frac{14±26}{4} = 10 ; - 3$

Ответ б