А)1-1,7х -0,8-2 =3,4
-1,7х=3,4 -1 +0,8+2
-1,7х=5,2
х=5,2 :(-1,7)=3,1...
Вот только подкорректируйте пункт б,т.к. без знака его не решишь.
2х - 3 = х + 7
2х - х = 7 + 3
х = 10
Уравнение имеет один корень
18 - 2x² = 0
2x² = 18
x² = 18 : 2
x² = 9
x = ±3
Ответ: х₁ = -3; х₂ = 3.
<span><span><span>х²-3х-40=0
</span></span></span>х₁+х₂=3 -- <span>теорема Виета</span>
х₁х₂= - 40
х₁=8
х₂= - 5
![D=b^{2}-4ac \\ x_{1}= \frac{-b- \sqrt{D} }{2a} \\ x_{2}= \frac{-b +\sqrt{D} }{2a} \\ \\ D=(-3)^{2}-4* (-40)=9+160=169 \\ x_{1}= \frac{-(-3)- \sqrt{169} }{2*1} = \frac{3-13}{2}= \frac{-10}{2} =-5 \\ x_{2}= \frac{-(-3)+ \sqrt{169} }{2*1} = \frac{3+13}{2}= \frac{16}{2} =8](https://tex.z-dn.net/?f=D%3Db%5E%7B2%7D-4ac+%5C%5C+x_%7B1%7D%3D+%5Cfrac%7B-b-+%5Csqrt%7BD%7D+%7D%7B2a%7D++%5C%5C+x_%7B2%7D%3D+%5Cfrac%7B-b+%2B%5Csqrt%7BD%7D+%7D%7B2a%7D++%5C%5C++%5C%5C+D%3D%28-3%29%5E%7B2%7D-4%2A%0A%28-40%29%3D9%2B160%3D169+%5C%5C+x_%7B1%7D%3D+%5Cfrac%7B-%28-3%29-+%5Csqrt%7B169%7D+%7D%7B2%2A1%7D++%3D+%5Cfrac%7B3-13%7D%7B2%7D%3D+%5Cfrac%7B-10%7D%7B2%7D+%3D-5++%5C%5C+x_%7B2%7D%3D+%5Cfrac%7B-%28-3%29%2B+%5Csqrt%7B169%7D+%7D%7B2%2A1%7D++%3D+%5Cfrac%7B3%2B13%7D%7B2%7D%3D+%5Cfrac%7B16%7D%7B2%7D+%3D8)