1.+ {-6х+у=21
+{6х-11у=-51
-10y=-30|:(-10)
y=3
-6x=21-3
-6x=18|:(-6)
x=-3
2.+ {9х+13у=35
+{29х-13у=3
38x=38|:38
x=1
13y=35-9
13y=26|:13
y=2
3. {5х+4у=-22
{5х-2у=-4|*2
+{5x+4y=-22
+{10x-4y=-8
15x=-30|:15
x=-2
4y=-22+10
4y=-12|:4
y=-3
Решите систему уравнений методом сложения!!!
1. {х-4у=9
{3х+2у=13|*2
+{x-4y=9
+{6x+4y=26
7x=35|:7
x=5
-4y=9-5
-4y=4|:(-4)
y=-1
2. {2х+у=6|*3
{-4х+3у=8
-{6x+3y=18
-{-4x+3y=8
10x=10|:10
x=1
y=6-2
y=4
Удачи! ( коротко, напишите минимум 20 символов )))
В равенстве слева сумма имеет общий член ![a_n=n(2n+1)](https://tex.z-dn.net/?f=a_n%3Dn%282n%2B1%29)
1) Базис индукции: ![n=1](https://tex.z-dn.net/?f=n%3D1)
![1\cdot (2\cdot 1+1)=\dfrac{1\cdot (1+1)\cdot (4\cdot 1+5)}{6}~~~\Rightarrow~~~ 3=3](https://tex.z-dn.net/?f=1%5Ccdot%20%282%5Ccdot%201%2B1%29%3D%5Cdfrac%7B1%5Ccdot%20%281%2B1%29%5Ccdot%20%284%5Ccdot%201%2B5%29%7D%7B6%7D~~~%5CRightarrow~~~%203%3D3)
2) Предположим, что и для
верно равенство
![1\cdot 3+2\cdot 5+...+k(2k+1)=\dfrac{k(k+1)(4k+5)}{6}](https://tex.z-dn.net/?f=1%5Ccdot%203%2B2%5Ccdot%205%2B...%2Bk%282k%2B1%29%3D%5Cdfrac%7Bk%28k%2B1%29%284k%2B5%29%7D%7B6%7D)
3) Индукционный переход: ![n=k+1](https://tex.z-dn.net/?f=n%3Dk%2B1)
![\underbrace{1\cdot 3+2\cdot 5+...+k(2k+1)}_{\frac{k(k+1)(4k+5)}{6}}+(k+1)(2k+3)=\dfrac{(k+1)(k+2)(4k+9)}{6}\\ \\\\\dfrac{k(k+1)(4k+5)}{6}+(k+1)(2k+3)=\dfrac{(k+1)(k+2)(4k+9)}{6}\\ \\ \\ (k+1)\left(\dfrac{k(4k+5)}{6}+2k+3\right)=\dfrac{(k+1)(k+2)(4k+9)}{6}\\ \\ \\ (k+1)\cdot \dfrac{4k^2+5k+12k+18}{6}=\dfrac{(k+1)(k+2)(4k+9)}{6}\\ \\ \\ \dfrac{(k+1)(4k^2+17k+18)}{6}=\dfrac{(k+1)(k+2)(4k+9)}{6}\\ \\ \\ \dfrac{(k+1)(k+2)(4k+9)}{6}=\dfrac{(k+1)(k+2)(4k+9)}{6}](https://tex.z-dn.net/?f=%5Cunderbrace%7B1%5Ccdot%203%2B2%5Ccdot%205%2B...%2Bk%282k%2B1%29%7D_%7B%5Cfrac%7Bk%28k%2B1%29%284k%2B5%29%7D%7B6%7D%7D%2B%28k%2B1%29%282k%2B3%29%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%5C%5C%20%5C%5C%5C%5C%5Cdfrac%7Bk%28k%2B1%29%284k%2B5%29%7D%7B6%7D%2B%28k%2B1%29%282k%2B3%29%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%5C%5C%20%5C%5C%20%5C%5C%20%28k%2B1%29%5Cleft%28%5Cdfrac%7Bk%284k%2B5%29%7D%7B6%7D%2B2k%2B3%5Cright%29%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%5C%5C%20%5C%5C%20%5C%5C%20%28k%2B1%29%5Ccdot%20%5Cdfrac%7B4k%5E2%2B5k%2B12k%2B18%7D%7B6%7D%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%5C%5C%20%5C%5C%20%5C%5C%20%5Cdfrac%7B%28k%2B1%29%284k%5E2%2B17k%2B18%29%7D%7B6%7D%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%5C%5C%20%5C%5C%20%5C%5C%20%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D%3D%5Cdfrac%7B%28k%2B1%29%28k%2B2%29%284k%2B9%29%7D%7B6%7D)
Равенство выполняется для всех натуральных n. Что и требовалось доказать.
Решение задания смотри на фотографии
Параллельные прямые имеют одинаковый коэффициент перед х.
<span>(c): y = 5 - 1/7x
</span><span> у = 3 - 1/7х
</span>
(b): y = x - 7
<span>(d): y = х + 5
</span>
<span>у = -7х - 14
</span><span>у = 5 - 7х
</span>
<span>(b): y = x - 7
</span> <span>у = х - 2/7</span>