Oblicz: a) ctg25°×ctg35°×ctg45°×ctg55°×ctg65°= b) sin²75°+sin²15°-2sin30°= c) (cos52°-cos38°)²+2sin38°×sin52°+2cos60°=

a)ctg25° * ctg35° * ctg45° * ctg55° * ctg65° = ctg25° * ctg35° * ctg45° * ctg(90°-35°) * ctg(90°-25°) = ctg25° * tg25° * ctg35° * tg35° * ctg45° = 1*1*1=1 b),c)sory ale to tych nie moge dojsc ale juz 1 masz:)