Sinacosa=1/2*sin2a
--------------------------------------
sin18*cos18*cos36=1/2*sin36cos36=1/4*sin72
<span>1) an= (n-1) / (3n+2)
п = 1 а1 = 0
п = 2 а2 = 1/8
п = 3 а3 = 2/11
п = 4 а4 = 3/14
п = 5 а5 = 4/17
(0; 1/8; 2/11; 3/14; 4/17)
2) </span><span>an=(-1)^(n-1)
п = 1 а1 = 1
п = 2 а2 = -1
п = 3 а3 = 1
п = 4 а4 = -1
п = 5 а5 = 1
(1; -1; 1; -1; 1)
</span>
Ответ:см прикрепленный файл
Объяснение:
![1)](https://tex.z-dn.net/?f=1%29)
![3^{x}=\frac{1}{9}](https://tex.z-dn.net/?f=3%5E%7Bx%7D%3D%5Cfrac%7B1%7D%7B9%7D)
![3^{x}=3^{-2}](https://tex.z-dn.net/?f=3%5E%7Bx%7D%3D3%5E%7B-2%7D)
![3=3=>x=-2](https://tex.z-dn.net/?f=3%3D3%3D%3Ex%3D-2)
Ответ: x= -2
![2)](https://tex.z-dn.net/?f=2%29)
![5^{x}=\sqrt{5}](https://tex.z-dn.net/?f=5%5E%7Bx%7D%3D%5Csqrt%7B5%7D)
![5^{x}=5^{1/2}](https://tex.z-dn.net/?f=5%5E%7Bx%7D%3D5%5E%7B1%2F2%7D)
![x=\frac{1}{2}=0,5](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B1%7D%7B2%7D%3D0%2C5)
Ответ: x= ¹/₂ иначе x=0,5
![3)](https://tex.z-dn.net/?f=3%29)
![7^{x}=3\sqrt{4}](https://tex.z-dn.net/?f=7%5E%7Bx%7D%3D3%5Csqrt%7B4%7D)
![7^{x}=3*2](https://tex.z-dn.net/?f=7%5E%7Bx%7D%3D3%2A2)
![7^{x}=6](https://tex.z-dn.net/?f=7%5E%7Bx%7D%3D6)
![x= log_76](https://tex.z-dn.net/?f=x%3D%20log_76)
Ответ: x=log₇6
![4)](https://tex.z-dn.net/?f=4%29)
![(\frac{2}{3})^x=1,5](https://tex.z-dn.net/?f=%28%5Cfrac%7B2%7D%7B3%7D%29%5Ex%3D1%2C5)
![(\frac{2}{3})^x=\frac{15}{10}](https://tex.z-dn.net/?f=%28%5Cfrac%7B2%7D%7B3%7D%29%5Ex%3D%5Cfrac%7B15%7D%7B10%7D)
![(\frac{2}{3})^x=\frac{3}{2}](https://tex.z-dn.net/?f=%28%5Cfrac%7B2%7D%7B3%7D%29%5Ex%3D%5Cfrac%7B3%7D%7B2%7D)
![(\frac{2}{3})^x=(\frac{2}{3})^{-1}](https://tex.z-dn.net/?f=%28%5Cfrac%7B2%7D%7B3%7D%29%5Ex%3D%28%5Cfrac%7B2%7D%7B3%7D%29%5E%7B-1%7D)
![x=-1](https://tex.z-dn.net/?f=x%3D-1)
Ответ: x= -1
-2x + y = 15 ,
-2x - y = 1 ; +
__________
-4x = 16
x = -4
Встовляем x в любое уравнение и находим y:
-2 * (-4) + y = 15
8 + y = 15
y = 7
Ответ: x = -4 , y = 7