а) воспользуемся формулой приведения: tg(x) = ctg(90°-x), тогда

ctg 2 *ctg 8 * сtg 14 ... *ctg 82 * ctg 88 = ctg 2 *ctg 8 * сtg 14 ... *ctg (90-8) * ctg (90-2) =  ctg 2 *ctg 8 * сtg 14 ... *tg 8 * tg 2.

Т.к. tg x * ctg x =1, то ctg 2 *ctg 8 * сtg 14 ... *tg 8 * tg 2 = 1

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б) (sin(x/2)+cos(x/2) )² = sin²(x/2)+2*sin(x/2)*cos(x/2) + cos²(x/2) = 1 + sin(x) = 1+0.21  =1.21

Тогда sin(x/2)+cos(x/2) = √1,21 = 1,1

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в) (sin(x/2)-cos(x/2) )² = sin²(x/2)-2*sin(x/2)*cos(x/2) + cos²(x/2) = 1 - sin(x) = 1-(-0.44)  =1.44

Тогда sin(x/2)-cos(x/2) = √1,44 = 1,2