A) A= tg²α(1 - sin²α) - sin²α = tg²α·cos²α - sin²α = (sin²α/cos²α) - sin²α = 0
b) A= √(sin²β+ sin²β·cosβ/sinβ +cos²β·sinβ/cosβ) =
= √[1+ 2sinβ·cosβ) = √(1+sin2β)
c) A = 9sin²α + 12sinα·cosα + 4cos²α + 4sin²α - 12sinα·cosα + 9cos²α =
= 13(sin²α +cos²α) = 13
d) a= ctgβ·tgβ/sinβ - cos²β/sinβ = (1 - cos²β)/sinβ = sin²β/sinβ = sinβ