tan13°×tan103°=?cos²π/8+cos²3π/8=?

问题描述:

tan13°×tan103°=?cos²π/8+cos²3π/8=?
(1)tan13°×tan103°=
(2)cos²π/8+cos²3π/8=
(3)sin²3°+sin²11°+sin²79°+sin²87°=

(1)=tan13°*(-cot13°)=-1
(2)=cos(π/8)^2+cos(π/2-π/8)^2=cos(π/8)^2+sin(π/8)^2=1
(3) =(sin3°)^2+cos(3°)^2+(sin11°)^2+(cos11°)^2=1+1=2.