(a+2b)² + (-8ab)= a²+4ab+4b²-8ab=a²-4ab+4b²=(a-2b)²
Ответ: В) -8ab
8/16=16/32
......................
...=p(в квадрате)-49q(в квадрате)
5.3x²+13x+4=0
D=169-48=121
![\sqrt{D}=11 \\ \\ x_{1}= \frac{-b-\sqrt{D}}{2a}= \frac{-13-11}{6}=-4 \\ \\ x_{2}=\frac{-b+\sqrt{D}}{2a}=\frac{-13+11}{6}=- \frac{1}{3} \\ \\](https://tex.z-dn.net/?f=+%5Csqrt%7BD%7D%3D11+%5C%5C++%5C%5C+%0A+x_%7B1%7D%3D+%5Cfrac%7B-b-%5Csqrt%7BD%7D%7D%7B2a%7D%3D+%5Cfrac%7B-13-11%7D%7B6%7D%3D-4+%5C%5C++%5C%5C+%0A+x_%7B2%7D%3D%5Cfrac%7B-b%2B%5Csqrt%7BD%7D%7D%7B2a%7D%3D%5Cfrac%7B-13%2B11%7D%7B6%7D%3D-+%5Cfrac%7B1%7D%7B3%7D+%5C%5C++%5C%5C+)
![ax^2+bx+c=a*(x-x_{1})*(x-x_{2}) \\ \\ 3*(x+\frac{1}{3})*(x+4)=(3x+1)(x+4) \\ \\](https://tex.z-dn.net/?f=ax%5E2%2Bbx%2Bc%3Da%2A%28x-x_%7B1%7D%29%2A%28x-x_%7B2%7D%29+%5C%5C++%5C%5C+%0A3%2A%28x%2B%5Cfrac%7B1%7D%7B3%7D%29%2A%28x%2B4%29%3D%283x%2B1%29%28x%2B4%29+%5C%5C++%5C%5C+)
7.
![\frac{5a^2-4}{4}+\frac{a+3}{5}=5|*20 \\ \\ 25a^2-20+4a+12=100 \\](https://tex.z-dn.net/?f=+%5Cfrac%7B5a%5E2-4%7D%7B4%7D%2B%5Cfrac%7Ba%2B3%7D%7B5%7D%3D5%7C%2A20+%5C%5C++%5C%5C+%0A25a%5E2-20%2B4a%2B12%3D100+%5C%5C)
25a²+4a-108=0
D=16+10800=10816
![\sqrt{D}=104 \\ \\ a_{1}= \frac{-4-104}{50}=-2,16 \\ \\ a_{2}= \frac{-4+104}{50}=2](https://tex.z-dn.net/?f=+%5Csqrt%7BD%7D%3D104+%5C%5C++%5C%5C+a_%7B1%7D%3D+%5Cfrac%7B-4-104%7D%7B50%7D%3D-2%2C16+%5C%5C++%5C%5C+a_%7B2%7D%3D+%5Cfrac%7B-4%2B104%7D%7B50%7D%3D2)
При a=-2,16; 2 сумма дробей равна 5.
7.
А)x²-9=0
x=+3
x=-3
Ответ:+3;-3.
Б)x²+2x=0
x*(x+2)=0
![x_{1}=0](https://tex.z-dn.net/?f=+x_%7B1%7D%3D0)
или
![x_{2}=-2](https://tex.z-dn.net/?f=+x_%7B2%7D%3D-2)
Ответ:0;-2.
В)x²+4=0
x²=-4
Нет корней.
Следовательно.
Ответ:А-3;Б-1;В-4.