cos2(π 4-a)-sin2(π 4 a)

y=-cos（2x+π2）=sin2x，∵ω=2，∴T=π，∵sin（-2x）=-sin2x，则函数y为周期为π的奇函数．故选A

tan(α+π/4)=(1+tanα)/(1-tanα)=(sinα+cosα)/(cosα-sinα)=(sinα+cosα)^2/(cosα^2-sinα^2)=(1+sin2α)/cos2α=(

tan(π/4+θ)=(tanπ/4+tanθ)/(1-tanπ/4tanθ)=(1+tanθ)/(1-tanθ)=2由此可以解出tanθ=1/3.万能公式cos2θ＝(1-tan^θ)/(1+tan

cos2(π/4-α)-sin2(π/4-α)=cos(π/2-2α）-sin(π/2-2α)=sin2α-cos2α=√2(√2/2sin2α-cos2α)=√2sin(2α-π/4)根据二倍角公式

题目写错了吧：应该是求证：sin2α+2cos2β=3证明：sin(π/4+α)=sinθ+cosθ(√2/2)(sina+cosa)=sinθ+cosθ两边同时平方得到：(1/2)(sin²

由两角和公式展开第一个等式得：根号2（sina+cosa）=sinθ+cosθ,再两边平方,得2(1+sin2a)=1+sin2θ得sin2a=(sin2θ-1)/2;cos2β=1-2sin^2β=

2sin（π/4＋α）=√2(sina+cosa)√2(sina+cosa)=sinθ＋cosθ将这个式子平方,得2(1+sin2a)=1+sin2θ2sin2β=sin2θ2(1+sin2a)=1+

(1)a·b=(cos2/3x,sin2/3x)*(cos2/x,-sin2/x)=cos2/3x*cos2/x-sin2/3x*sin2/x=cos(2/3x+2/x)=cos8/3x|a+b|=√

1f(x)=a·b+2λ|a+b|a·b=(cos(3x/2),sin(3x/2))·(cos(x/2),-sin(x/2))=cos(2x)|a+b|^2=|a|^2+|b|^2+2a·b=2+2c

由直角得：OA·OB=(a-b)(a+b)=a²-b²=0∴‖a‖=‖b‖由等腰得：‖OA‖=‖OB‖即‖a-b‖=‖a+b‖∴√（a-b）²=√（a+b）²∴

a=(cos3x/2,sin3x/2),b=(cosx/2,-sinx/2),(1)a*b=(cos3x/2,sin3x/2)*(cosx/2,-sinx/2)=cos(3x/2)*cos(x/2)-

sinπ=0cosπ=-1sin2π=0cos2π=1

∵tan（π4+α）=tanπ4+tanα1−tanπ4tanα=1+tanα1−tanα=12，∴3tanα=-1，解得：tanα=-13；∴sin2α−cos2α1+cos2α=2sinαcosα

题目是这样吧【tan(2α+π∕4)+6sin2α-cos2α】∕【3sin2α-2cos2α】方法是用辅助角公式展开tan2A=2tanA/(1-(tanA)^2);tan(A+B)=(tanA+t

原式=cos[2(π/4-a)]=sin(2a)公式：cos2x=(cosx)^2-(sinx)^2

tan(α+π/4)=(1+tanα)/(1-tanα)=(sinα+cosα)/(cosα-sinα)=(sinα+cosα)^2/(cosα^2-sinα^2)=(1+sin2α)/cos2α=(

设A=α+π/4,2A=2α+π/2tan(2A)=tan(2α+π/2)=-cot(2α)=-cos2α/sin2α=-b/atan(2A)=2tanA/(1-tanA^2)=-b/a解之得[2a+

tan[π/4+α]=(tanπ/4+tanα)/(1-tanπ/4tanα)=(1+sinα/cosα)/(1-sinα/cosα)=(cosα+sinα)/(cosα-sinα)=[2cos^2(

tan(θ+π/4)=sin(2θ+π/2)/[1+cos(2θ+π/2)]=cos(2θ)/[1-sin(2θ)]=b/[1-a]ortan(θ+π/4)=[1-cos(2θ+π/2)]/sin(2

tan(π/4－a)=[1－tana]/[1＋tana]=3,则tana=－1/2.而sin2a－coa2a=[2sinacosa－cos²a＋sin²a]/[sin²a