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Cos3x=cos15x
cos3x-cos15x=0
2sin6xsin9x=0
sin6x=0⇒6x=πn⇒x=πn/6
sin9x=0⇒9x=πn⇒x=πn/9
x=π/9-наим
1)-1/2
2)-√2 /2
3)-√3 /3
4)-1
№3:
Tg 17p/6=tg(2p+p-p/6 )=tg(p/6)=-√3 /3
№2:
sin(-11p/4)=sin(2p-3p/4)=sin(3p/4)=-√2 /2
F'(x) = 1,5(sin2x)' - 5(sinx)' - x' = 3cos2x - 5cosx - 1
f''(x) = 3(cos2x)' - 5(cosx)' -1' = -6sin2x + 5sinx = 0
5sinx - 6(2sinxcosx) = 0
5sinx - 12sinxcosx = 0
sinx(5-12cosx)=0
5-12cosx=0
12cosx=5
cosx=5/12=0.416
x = acos(0.416) = 65.4