sin(20°+a)=1/3,则cos(110°+a)的值是多少?饿救命!

已知 sin a-cos a=1/2,则 sin^3 a-cos^3 a 已知sin(70°+a)=1/3,则cos(a-20°)=? 若tana=1/3,则sin^3 a+2cos^ 3 a/sin^3 a-2cos^3 a 已知cos(75°+a)=1/3,则sin(a-15°)+cos(105°-a)的值 tana=m 则[sin(a+3pai)+cos(pai+a)]/[sin(-a)-cos(pai+a)] 设角a=-35π/6,则2sin(π+α)cos(π-α)-cos(π+α)/ 1+sin^2α+sin(π-α)-cos^2(π+α)sina=sin(-35π/6)=sin(-6π+π/6)=1/2 cosα=根号3/22sin(π＋α)cos(π-α)-cos(π+α)/ [1+sin^2α+sin(π-α)-cos^2(π+α)]=2（-sinα)(-cosα）+cosα/[1+sin² 由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证：1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a) 若cos(A+B)cos(A-B)=1/3 则cos平方A－sin平方B 等于 已知cos(a+b)cos(a-b)=1/3,则cos^2a-sin^2b的值是? 若cos(a+b)cos(a-b)=1/3,则cos²a-sin²b的值 已知cosа=-1/3 则 sin（30°+a）+sin(30°-a)的值是 sin(a-b)*cos a-cos(a-b)*sin a=1/5,则cos 2b的值是 求证1+sin a+cos a+2sin acos a/1+sin a+cos a=sin a+cos a 已知tanα=1/2,则((1/4)sin^2)((1/4)sin^2A+(3/4)cos^2A)/(sin^2A-cos^2A) sin(75°+a)=1/3,则cos(15°-a)= 求证1/sin^2a+3/cos^2a>=4+2根号下31/sin²a +3/cos²a=(sin²a+cos²a)/sin²a +3(sin²a+cos²a)/cos²a=1+cos²a/sin²a+3+3sin²a/cos²a=4+cos²a/sin²a+3sin²a/cos²a≥4+2√[(cos sin(20°+a)=1/3,则cos(110°+a)的值是多少?饿救命! 求证:sin 2a/1+sin a+cos a=sin a+cos a-1急