2cos^2x -3cosx=0
2(1-sin^2x)-3cosx=0
2-2cos^2x-3cosx+=0
-2cos^2x-3cosx+2=0
2cos^2x+3xcos-2=0
D=9-4(-2*2)=9+16=25
cosx1=(-3+5)/4=2/4=1/2
cos2=(-3-5)/4=-8/4=-2
x=1/2
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F(x)=1/(sinx*cosx)
sinx*cosx≠0
sinx≠0 ∧ cosx≠0
x≠πn, n∈Z x≠π/2+πn, n∈Z
D(f)=R-{πn; π/2+πn}, n∈Z