Сos(t - 2π) = cos(2π - t) = cost
cos^2t = 1/(tg^2t + 1)
cos^2t = 1/(5/4 + 1)
cos^2t = 4/9
cost = -(2/3)
cost = (2/3)
ctg(-1) = - ctgt, tgt = -√5/2, tgt*ctgt = 1,ctgt = 1/tgt, ctgt = 1/(-√5/2)
sin(4π - t) = sint
sint = √(1 - cos^2x) = √[1 - (2/3)^2] = √5/3
<span> 4х-3(х-7)=2х+15</span>
<span>4х-3х+21=2х+15</span>
<span>-Х=15-21</span>
<span>х=6</span>
<span>Sin2x = tgx
2sinxcosx=sinx/cosx
Умножаем обе части на cosx
2sinxcos</span>²x=sinx
2sinxcos²x-sinx=0
Выносим за скобку sinx
sinx(2cos²x-1)=0
sinx=0 или 2сos²x-1=0
x=Пn, n∈z 2cos²x=1
cos²x=1/2
x=+- П/4+ 2Пk, k∈z
Ответ: x=Пn, n∈z ; x=+- П/4+ 2Пk, k∈z
В радианах √3/2≈0.86 или можно взять 0.87
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