6х-2у-5=2х-3у
У=-4х+5
5-х+2у=4у+16
-х-2у-11=0
-х-2(-4х+5)-11=0
7х=21
Х=3
У=-7
Ответ (3;-7)
⁴√ [(-3)² * 2] * ⁴√ (8 * 9) = ⁴√( 9 * 2) * ⁴ (8 * 9) = ⁴√ (9 * 2 * 8 * 9) =
= ⁴√ (3⁴ * 2⁴) = 3 * 2 = 6
8 восьмерок => 8+8 =16 88+88=176 888+8+8+88+8+8
На фото............................................................................
![3\cos 2x = 7\cos x \\ 3(2\cos ^{2}x - 1) - 7\cos x = 0 \\ 6\cos ^{2}x - 3 - 7\cos x = 0 \\ \cos x = t \\ 6t^{2}-7t-3=0 \\ D = 49 + 24*3 = 121 \\ \\ t_{1} = \dfrac{7 + 11}{12} = 1.5 \ ; \ \ \ t_{2} = \dfrac{7-11}{12} = -\dfrac{1}{3} \\ \\ $\left[ \begin{gathered} \cos x = 1.5 \\ \cos x = -\dfrac{1}{3} \\ \end{gathered} \right.$ \ \ \ ; \ $\left[ \begin{gathered} x \notin [-1;1] \\ x = \pm \arccos( -\dfrac{1}{3}) + 2\pi n, n \in Z \end{gathered} \right.$](https://tex.z-dn.net/?f=+3%5Ccos+2x+%3D+7%5Ccos+x+%5C%5C+3%282%5Ccos+%5E%7B2%7Dx+-+1%29+-+7%5Ccos+x+%3D+0+%5C%5C+6%5Ccos+%5E%7B2%7Dx+-+3+-+7%5Ccos+x+%3D+0+%5C%5C+%5Ccos+x+%3D+t+%5C%5C+6t%5E%7B2%7D-7t-3%3D0+%5C%5C+D+%3D+49+%2B+24%2A3+%3D+121+%5C%5C+%5C%5C+t_%7B1%7D+%3D+%5Cdfrac%7B7+%2B+11%7D%7B12%7D+%3D+1.5+%5C+%3B+%5C+%5C+%5C+t_%7B2%7D+%3D+%5Cdfrac%7B7-11%7D%7B12%7D+%3D+-%5Cdfrac%7B1%7D%7B3%7D+%5C%5C+%5C%5C+%24%5Cleft%5B++++++++%5Cbegin%7Bgathered%7D++++++++++%5Ccos+x+%3D+1.5+%5C%5C+%5Ccos+x+%3D+-%5Cdfrac%7B1%7D%7B3%7D+%5C%5C++++++++%5Cend%7Bgathered%7D++%5Cright.%24++%5C+%5C+%5C+%3B+%5C++%24%5Cleft%5B++++++++%5Cbegin%7Bgathered%7D++++++++++x+%5Cnotin+%5B-1%3B1%5D+%5C%5C+x+%3D+%5Cpm+%5Carccos%28+-%5Cdfrac%7B1%7D%7B3%7D%29+%2B+2%5Cpi+n%2C+n+%5Cin+Z+++++++%5Cend%7Bgathered%7D++%5Cright.%24++++)
Ответ: x = arccos(-1/3) + πn, n∈Z