Question

Помогите с алгеброй, пожалуйста..

Answer 1

$\displaystyle\bf\\x^{2} -\underbrace{9,9}x-3,9=0\\\\x_{1} +x_{2} =9,9\\\\\\x^{2} -9,9x\underbrace{-3,9}=0\\\\x_{1} \cdot x_{2} =-3,9\\\\\\2)\\\\x_{1} =-3 \ \ ; \ \ x_{2} =-17 \ \ a=1\\\\x_{1} +x_{2} =-3-17=-20\\\\x_{1} \cdot x_{2} =-3\cdot(-17)=51\\\\x^{2} +20x+51=0$

Answer 2

Ответ:

1.

${x}^{2} - 9.9x - 3.9 = 0 \\ d = {b}^{2} - 4ac = {( - 9.9)}^{2} - 4 \times 1 \times ( - 3.9) = \\ { ( - \frac{99}{10} )}^{2} + 4 \times \frac{39}{10} = \frac{9801}{100} + \frac{156}{10} = \\ \frac{9801 + 1560}{100} = \frac{11361}{100} = 113.61 \\ x1 = \frac{ - b - \sqrt{d} }{2a} = \frac{ - ( - 9.9) - \sqrt{113.61} }{2 \times 1} = \\ \frac{9.9 - \sqrt{113.61} }{2} \\ x2 = \frac{ - b + \sqrt{d} }{2a} = \frac{ - ( - 9.9) + \sqrt{113.61} }{2 \times 1} = \\ \frac{9.9 + \sqrt{113.61} }{2}$

$x1 + x2 = \frac{9.9 - \sqrt{113.61} }{2} + \frac{9.9 + \sqrt{113.61} }{2} = \\ \frac{9.9 + 9.9}{2} = \frac{19.8}{2} = 9.9$

$x1 \times x2 = \frac{9.9 - \sqrt{113.61} }{2} \times \frac{9.9 + \sqrt{113.61} }{2} = \\ \frac{(9.9 - \sqrt{113.61})(9.9 + \sqrt{113.61}) }{4} = \\ \frac{9.9 \times 9.9 + 9.9 \times \sqrt{113.61} - \sqrt{113.61} \times 9.9 - \sqrt{113.61} \times \sqrt{113.61} }{4} = \\ \frac{98.01 - 113.61}{4} = \frac{ - 15.6}{4} = - 3.9$

2.

$(x + 3)(x + 17) = \\ x \times x + x \times 17 + 3 \times x + 3 \times 17 = \\ {x}^{2} + 17x + 3x + 51 = \\ {x}^{2} + 20x + 51$

Ответ:

${x}^{2} + 20x + 51 = 0$