A) tg(180 - a) / ctg (90 - a) = -tg a / tg a = -1
б) (cos²(90 - α )-1) / cos (180 - α) = (sin<span>² α -1) / (-cos α) = </span>- cos² α / (-cos α) = cos a
в) sin (π-α) / tg (π+a) = <span>sin α / tg a = </span><span>sin α cos a / sin a</span> = cos a
A=2.5 (2.5\(2.5-2))-((2.5-5)\2.5)=5-(-1)=6