Question

cos^2(90+a) + cos^2(180-a) + tg (270-a)×tg(180+a)

Answer 1

Cos²(90° + α) + Cos²(180° - α) + tg(270° -α) * tg(180° + α) =

= Sin²α + Cos²α + Ctgα * Tgα = (Sin²α + Cos²α) + (Ctgα * Tgα) = 1 + 1 = 2