cos2a/sina+π/4=1/2求cos2a

cos2a/sina+π/4=1/2求cos2a 1-cos2a/sina=2sina【过程,】 求证 1-cos2a/sina=2sina sina+cosa=1/2,求cos2a的值 sinA=1/3,求cos2A 已知sinA=2/3,求cos2A 必修四的数学题,sina+sin2a=1求3cos2a+cos2a-2sina+1的值 已知sina-cosa=-2cos2a求sina+cosa=? 已知（2sinA+cosA)/(sinA-cosA)=-5 求1、(sinA+cosA)/(sinA-cosA) 2、3cos2A+sin2A 已知tana=2求2sina-cosa/sina+cosa求1-2sinacosa/sin2a-cos2a sina+cosa=1/5且2a∈（π,3π/2)求cos2a,tan(2a-π/4) 若cos2a/sin(a-π/4)=-根号2/2 求：1.cosa+sina；2.cosa-sina; 3.tana 已知cos2a=4/5,且2a属于{π,2π},求sina 已知cos2a=3/4,且π＜a＜3π/2,求sina,cosa, 已知a属于(π,2π)且cosa-sina=1/3求cos2a的值 若 cos2a/sin（a-π/4)= -√2/2,求cosa+sina的值. 已知a属于0到2π,sina+cosa=1/5,求sin2a和cos2a tanA=1/2求2sin2A-3sinA乘cosA-4cos2A