cos3x*cosx = cos2x
1/2*[cos(3x-x) + cos(3x + x)] = cos2x
cos2x - cos4x = 2 cos2x
cos4x - cos2x = 0
2*[sin(4x + 2x)/2 * sin(2x - 4x)/2] = 0
1) sin3x = 0
3x = πn, n∈Z
x = πn/3, n∈z
2) sinx = 0
x = πk, k∈Z
Пусть ∠(cb)=х°, тогда
∠(ac)=х+20
∠(cb)+∠(ac)=180°(смежные)
х+х+20=180
2х=180-20
2х=160
х=160:2
х=80
∠(cb)=80°, ∠(ac)=80+20=100°
2с*3с^2*4^3 = 2с*3с²*4³ = 384с³
11) 2·10у+3у=16,20у+3у=16 , 23у=16, у=16/23