化简(1)cos^2(π/4-a)+cos^2(π/4+a);(2) cos[(4n+1)/4*π+a]+cos[(4n-1)/4*π-a] (n属于z)

问题描述:

化简(1)cos^2(π/4-a)+cos^2(π/4+a);(2) cos[(4n+1)/4*π+a]+cos[(4n-1)/4*π-a] (n属于z)

(2cos²a-1)/[2tan(π/4-a)*sin²(π/4+a)] =cos2a/[2tan(π/4-a)*cos²(π/4-a)] =cos2a/[2sin(π/4-a)*cos(π/4-a)] =cos2a/sin(π/2-2a) =cos2a/cos2a =1