sin^220°+cos^250°+sin30°sin70°

sin^220°+cos^250°+sin20°cos50° sin^220°+cos^250°+sin30°sin70° 化简3/(sin^220°)-1/(cos^220°)+64sin^220° sin(10°)+sin(20°)cos(50°)求值 cos^15°-sin^15°= sin(α+30°)-sin(α-30°)/cosα sin^2 30°+cos()=1 计算：sin^67.5°-cos^67.5度 sin²15° 把sin变成带cos的 观察下列等式：①sin²10°＋cos²40＋sin10°cos40°＝3／4；②sin²6°＋cos²36°＋si②sin²6°＋cos²36°＋sin6°cos36°＝3／4。由上面两式的结构规律，你是否能提出一个猜想？并证明 sin(-1200°)-cos1290°+cos(-120)°+cos(-1020)°-sin(-1050°)+tan855° Cos(180°+α)*sin（α+360°)/sin(-α-180°)*cos(-180°-α) sin(33°-x)cos(27°+x)+cos(33°-x)sin(27°+x) sin(-120°)cos(1290°)+cos(-1020°)sin(-1050°)= sin(70° a)cos(10° a)-cos(70° a)sin(170°-a) sin(a+45°)sin(a+15°)+cos(a+45°)cos(a+15°) cos(α+30°)cosα+sin(α+30°)sinα等于? sin(α+30°)cosα+cos(α+30°)sinα=