Cos3x*cosx+sin3x*sinx=cos2x
-1-9=-10
X^2 + 4x + 4 - (16 - 8x + x^2) = 8;
x^2 + 4x + 4 - 16 + 8x - x^2 = 8;
12x = 8 - 4 + 16;
12x = 20;
x = 20/12
x = 1,66...(примерно)
Подобие треугольников.
х:2,3 = 14:8
х = 2,3*14 : 8 = 4,025
1/xˇ3 . 1/xˇ7= 1/xˇ10=xˇ(-10)