Question

Решите с 3 по 8. Заранее спасибо.

Answer 1

3) cos 2*20/(cos20-sin20) = (cos²20-sin²20)/(cos20-sin20)=(cos20-sin20)(cos20+sin20)/(cos20-sin20)= cos20+sin20

4)cos² π/12- sin² π/12 =cos 2* π/12 = cos π/6 = cos 30 = √3/2

5) 2cos35/sin2*35 = 2cos35/ 2sin35cos35 = 1 /sin35 

6) 1- 2sin² π/8 = cos 2* π/8 = cos π/4 = √2/2

7)-(2cos²75-1)=-cos2*75=-cos150=-(-√3/2)=√3/2

8)2*(1-2sin²a)+2sin²a-3=2-4sin²a+2sin²a-3=-1-2sin²a +2-2=1-2sin²a-2=cos2a-2