Ctgβ - sin 2β - ctgβ × cos 2β решите подробно.

= ctgβ(1-cos2β) - sin2β = ctgβ(1-(1-2sin²β)) -sin2β = ctgβ(1-1+2sin²β) - sin2β = ctgβ* 2sin²β - sin2β = (cosβ/sinβ)*2sin²β - sin2β = 2cosβ*sinβ - sin2β = sin2β-sin2β = 0