1-2sin22.5°和1-2cos^2 22.5°
计算:sin21°+sin22°+sin23°+…+sin287°+sin288°+sin289°.
Cos(a+b)*cos(a-b)=1/5 求cos ^2-sin^2
求证cos(720°+α)(2/cosα+tanα)(1/cosα-2tanα)=2cosα-3tanα
cos x>-1/2
计算:sin21°+sin22°+sin23°+…+sin288°+sin289°+sin290°= ___ .
若sina+sin^2a=1,求cos^2a+cos^4a的和
2(cos x)^2=1+cos 2x,
∫ (1+cos^2 x)/cos^2 x dx =
三角函数的值域 3cos+1/cos+2
2cos x (sin x -cos x)+1
tanα=-1/3,(1)(sinα+2cosα)/(5cos-sinα),(2)1/(2sinαcosα+cos^2α
已知tanα=1/3,计算(1)sinα+2cosα/5cosα-sinα,(2)1/2sinαcosα+cos^α