![2x^2-7x-4 \leqslant 0 \\ D=49+32=81 \\ x_1=\frac{7-9}{4}=-0,5 \\ x_2=\frac{7+9}{4}=4 \\ 2(x+0,5)(x-4)\leqslant 0](https://tex.z-dn.net/?f=2x%5E2-7x-4+%5Cleqslant+0+%5C%5C+D%3D49%2B32%3D81+%5C%5C+x_1%3D%5Cfrac%7B7-9%7D%7B4%7D%3D-0%2C5+%5C%5C+x_2%3D%5Cfrac%7B7%2B9%7D%7B4%7D%3D4+%5C%5C+2%28x%2B0%2C5%29%28x-4%29%5Cleqslant+0)
--(+)--(●-0,5)---(-)-----(●4)---(+)--->
![x\in[-0,5 ; 4]](https://tex.z-dn.net/?f=x%5Cin%5B-0%2C5+%3B+4%5D+)
<span>(a + 2b)² - (a + b)(b + a) = а</span>² + 4ab + b² - (a + b)² = а<span>² + 4ab + b² - a</span>² - 2ab - b² = 2ab
при а =1 и b = 1/5
2ab = 2 · 1 · 1/5 = 2/5
По дискриминанту = b^2-4ac=9+28=√37
x1,= (-3+√37)/2
x2=(-3-√37)/2
x1+x2= дальше прикрепляю рисунок