sina和cos2a

sinA*(1+cos2A)化简,原式=sinA(1+cos²A-sin²A）=sinAX2cos²A=sin(2A).cosA

(cosA-cos2A)/(sinA+sin2A)=?(cosA-2cos²A+1)/(sinA+2sinAcosA)=(cosA-cos²A+1-cos²A)/[sinA(1+2cosA)]=[cosA(1-

sina=cos2a求tanasina=cos2a=1-2sin²a2sin²a+sina-1=0(2sina-1)(sina+1)=0sina=1/2,sina=-1sin²a+cos²a=1所以c

求sinacos2a的值

化简（sin2acosa-sina）/cos2a（sin2acosa-sina）/cos2a=(2sinacosacosa-sina)/(2cos²a-1)=sina(2cos²a-1)/(2cos²a-1)=

1-cos2a/sina=2sina【过程,】1-cos2a/sina=（2sin²a）/sina=2sina要记住1-cos2a=2sin²a

求证1-cos2a/sina=2sina根据三角函数二倍角公式,cos2a=1-2(sina)^2所以1-cos2a/sina=1-[1-2(sina)^2]/sina=1-1+2sina=2sina

已知a属于0到2π,sina+cosa=1/5,求sin2a和cos2a将sina+cosa=1/5平方,1+2sinacosa=1/25,sin2a=-24/25,所以2a为第三、四象限角.当2a为第三象限角时,cos2a=-7/25,当

cos2a/sina+π/4=1/2求cos2acos2a=1-(sina)^2下面求sina1-（sina）^2=(1/2-π/4)sina这是一个关于sina的一元二次方程.既然提出这类问题,楼主应该知道下面该怎么做了吧.

(sina*sina-cosa*cosa)/cos2a*sina+cos2a*cosa)=0≤a≤π原式=-(cos2a-sin2a)/[cos2a(sina+cosa)]=-cos2a/[cos2a(sina+cosa)]=-1/(sin

(sina+sin2a)/(1+cosa+cos2a)化简(sina+sin2a)/(1+cosa+cos2a)＝(sina+2sinacosa)/(1+cosa+2(cosa)^2-1)=sina(1+2cosa)/cosa(1+2cos

化简：(sina+sin2a)/1+cosa+cos2a

sin2a+sina/cos2a+cosa+1=sin2a+sina/cos2a+cosa+1=(2sinacosa+sina)/(2cos²a+cosa)=sina(2cosa+1)/[cosa(2cosa+1)]=sina/c

求证：sina(1+cos2a)=sin2a*cosa.sina(1+cos2a)=sina(1+2cos^2a-1)=(2sina*cosa)*cosa=sin2a*cosasina(1+cos2a)=sina(1+2cos^2a-1)=

sinA=1/3,求cos2AsinA=1/3则cos2A=1-2sin²A=1-2*(1/3)²=1-2/9=7/9cos2A=1-2sin^2A=1-2(1/3)^2=1-2/9=7/9sinA=1/3A=30度co

1+2(sina^2)+cos2a=,急1+2sin²a+cos(2a)=1+[1-cos(2a)]+cos(2a)=1+1-cos(2a)+cos(2a)=2提示：就是利用公式：2sin²a=1-cos(2a)cos2

已知sinA=2/3,求cos2AsinA=2/3,cos2A=1-2sin²A=1-2*(2/3)²=1-8/9=1/9Cos2A=CosA^2-SinA^2=1-2SinA^2=1-2x(2/3)^2=1/9sinA

求三角函数最值cos2a+3sinacos2a+3sina=1-2(sina)^2+3sina=-2[(sina)^2-3/2sina+9/16]+9/8+1=-2(sina-3/4)^2+17/8-1cos2a+3sina=1-2(sin

解方程cos2A=cosA+sinA即cos²a-sin²a=cosa+sina(cosa+sina)(cosa-sina)=cosa+sina所以cosa+sina=0或cosa-sina=1√2sin(x+π/4)=

tana=2,则(sina+cosa)/(sina-cosa)+cos2a=?(sina+cosa)/(sina-cosa)+cos2a(分子分母同时除以cosa）=(sina/cosa+cosa/cosa)/(sina/cosa-cosa