![{x}^{4} - 2 {x}^{2} - 8x - 3 = 0 \\ {x}^{4} - 2 {x}^{3} + 2 {x}^{3} - {x}^{2} - 4 {x}^{2} + 3 {x}^{2} - 2x - 6x - 3 = 0 \\ {x}^{2} ( {x}^{2} - 2x - 1) + 2x( {x}^{2} - 2x - 1) + 3( {x}^{2} - 2x - 1) \\ ( {x}^{2} + 2x + 3)( {x}^{2} - 2x - 1) = 0 \\ {x}^{2} + 2x + 3 = 0 \\ {x}^{2} - 2x - 1 = 0 \\ d = {b}^{2} - 4ac = { (- 2)}^{2} - 4 \times 1 \times ( - 1) = 4 + 4 = 8 \\ x1 = \frac{2 + \sqrt{8} }{2} \\ x2 = \frac{2 - \sqrt{8} }{2} \\ x1 = \frac{2 + 2 \sqrt{2} }{2} = 1 + \sqrt{2} \\ x2 = \frac{2 - 2 \sqrt{2} }{2} = 1 - \sqrt{2}](https://tex.z-dn.net/?f=+%7Bx%7D%5E%7B4%7D++-+2+%7Bx%7D%5E%7B2%7D++-+8x+-+3+%3D+0+%5C%5C++%7Bx%7D%5E%7B4%7D++-+2+%7Bx%7D%5E%7B3%7D++%2B+2+%7Bx%7D%5E%7B3%7D++-++%7Bx%7D%5E%7B2%7D++-+4+%7Bx%7D%5E%7B2%7D++%2B+3+%7Bx%7D%5E%7B2%7D++-+2x+-+6x+-+3+%3D+0+%5C%5C++%7Bx%7D%5E%7B2%7D+%28+%7Bx%7D%5E%7B2%7D++-+2x+-+1%29+%2B+2x%28+%7Bx%7D%5E%7B2%7D++-+2x+-+1%29+%2B+3%28+%7Bx%7D%5E%7B2%7D++-+2x+-+1%29+%5C%5C+%28+%7Bx%7D%5E%7B2%7D++%2B+2x+%2B+3%29%28+%7Bx%7D%5E%7B2%7D++-+2x+-+1%29+%3D+0+%5C%5C++%7Bx%7D%5E%7B2%7D++%2B+2x+%2B+3+%3D+0+%5C%5C++%7Bx%7D%5E%7B2%7D++-+2x+-+1+%3D+0+%5C%5C++d+%3D++%7Bb%7D%5E%7B2%7D++-+4ac+%3D++%7B+%28-+2%29%7D%5E%7B2%7D+-+4+%5Ctimes+1+%5Ctimes+%28+-+1%29+%3D+4+%2B+4+%3D+8++%5C%5C+x1+%3D++%5Cfrac%7B2+%2B++%5Csqrt%7B8%7D+%7D%7B2%7D++%5C%5C+x2+%3D++%5Cfrac%7B2+-++%5Csqrt%7B8%7D+%7D%7B2%7D++%5C%5C+x1+%3D++%5Cfrac%7B2+%2B+2+%5Csqrt%7B2%7D+%7D%7B2%7D++%3D+1+%2B++%5Csqrt%7B2%7D++%5C%5C+x2+%3D++%5Cfrac%7B2+-+2+%5Csqrt%7B2%7D+%7D%7B2%7D++%3D+1+-++%5Csqrt%7B2%7D+)
Ответ: х1 = 1+√2 ; х2 = 1-√2
(0.8x+19.4)*0.2=1.928
0.8x*0.2+19.4*0.2=1.928
0.16x+3.88=1.928
0.16x=1.928-3.88
0.16x=-1.952
x=-12.2
1) 9-3=6(см) - ширина
2) 2*(9+6)=30(см)-периметр
3) 9*6=54(см²)-площадь
2 2/6 - 1 3/6
4 2/10 - 2 3/10
7 1/9 - 4 3/9
2 10/35 - 1 21/35
6 5/20 - 3 8/20