а) sin²a+2sinacosa+cos²a+sin²a-2sinacosa+cos²a= sin²a+cos²a+sin²a+cos²a= 1+1= 2
б) tg²a+2tgactga+ctg²a+tg²a-2tgactga+ctg²a= tg²a+ctg²a+tg²a+ctg²a= 2(tg²a+ctg²a)= 2(1/cos²a -1+ 1/sin²a -1)= 2(1/cos²a + 1/sin²a -2)= 2((sin²a+cos²a-2sin²acos²a)/sin²acos²a))= 2((1-2sin²acos²a)/sin²acos²a))= 2((1-cos2a)/cos2a))= (2/cos2a)-2
в) sina(2+cosa/sina)(2cosa/sina+1)-5cosa= sina((2sina+cosa)/sina)*((2cosa+sina)/sina)-5cosa= (4sinacosa+2sin²a+2cos²a+sinacosa)/sina - 5cosa= (5sinacosa+2)/sina -5cosa= 5cosa+ 2/sina -5cosa= 2/sina
