Question

Номера 11, 14, 15!

Срочно! Пожалуйста!

Answer 1

1)   (1-cos²x)×ctg²x-1
       sin²x+cos²x=1
       cos²x-1=sin²x
       sin²x×cos²x/ sin²x=1
        cos²x-1=-sin²x

Answer 2

$1) (1-cos^{2} x)*ctg^{2} x-1=(sin^{2} x+cos^{2} x-cos^{2} x)*ctg^{2} x-1= \ =sin ^{2} x*ctg ^{2} x-1=sin ^{2} x* frac{cos^{2} x}{sin ^{2} x} -1=cos^{2} x-1=-(1-cos ^{2} x)= \ =-sin^{2} x$