Может ты имел в виду cos20*cos40*cos80
<em>5)</em>
ctg x = 1
x = π/4 + πn, n є Z
tg x = -1
x = -π/4 + πk, k є Z
cos x = 0
x = π/2 + πn, n є Z
sin x = 1
x = π/2 + 2πk, k є Z
<em>6)</em>
7^x = 49
7^x = 7^2
x = 2
log_5 x = 4
5^4 = x
5^4 = 625
√(x-3) = 7
x-3 = 49
x = 52
<em>7)</em>
y=x^95 - cos x
y' = 95x^94 + sin x
y=x^5 - sin x
y' = 5x^4 - cosx