已知yana=4√3,cos(a b)=-11 14.a,b均为锐角

cosα+cosβ=3/5sinα+sinβ=4/5两边平方cos²α+2cosαcosβ+cos²β=9/25sin²α+2sinαsinβ+sin²β=16

原式=3cos²α-2sinα×cosα-4cos²α-6(sin²α+cos²α)=-6sin²α-2sinαcosα-7cos²α=(-

再问：再问：在你答题的时候我蛋疼做了一遍，结果好像不一样……再问：不过还是辛苦施主了

π/2

要知道这章的知识非常灵活,多见见题型就行了.β=[α-(α-β)]这个知道吧?因为0

f(x)=2sin(x/4)cos(x/4)+(√3)cos(x/2)=sin(x/2)+(√3)cos(x/2)=2sin(x/2+π/3)T=4π最大值2最小值-2（2）令g(x)=f(x+π/3

∵sinθ+cosθ=√2/3∴（sinθ+cosθ）²=2/9sin²θ+2sinθcosθ+cos²θ=2/9∵sin²θ+cos²θ=1∴1+2

两倍角公式2cos²x=cos2x+12sinxcosx=sin2xf(x)=-4cos²x+4√(3)sinxcosx+5=-2(cos2x+1)+2√3sin2x+5=2√3s

因为π/4+x和π/4-x是互余的（和是π/2）,所以cos(π/4+x）=sin(π/4-x)=3/5因为0＜x＜π/4所以sin(π/4+x)=4/5(因为π/4+x为第一象限角)

sinα+sinβ=3/5,则(sinα+sinβ)^2=9/25,即(sinα)^2+(sinβ)^2+2sinαsinβ=9/25,同理cosα+cosβ=4/5,则(cosα+cosβ)^2=1

cos2x=3/5,sin2x=±4/5sin^4x+cos^4x=（-sinx^2+cosx^2)^2+2sinx^2cosx^2=cos2x^2+1/2sin2x=9/25±2/5=19/25,或

3sinacosa=3sinacosa/（sin²a+cos²a）分子分母同时除以cos²a得原式=3tana/（tan²a+1）=-12/17再问：那个同时除

(sinθ+cosθ)²=16/9sinθ²+cosθ²+2sinθcosθ=16/92sinθcosθ=7/9sinθ-cosθ=根号下（sinθ-cosθ）²

17pi/12

sinα+cosβ=3/5…①cosα+sinβ=4/5...②①²+②²,2+2(sinαcosβ+cosαsinβ)=1∴sin(α+β)=-1/2.①²-②

f(x)=2√3sinxcosx-2cos(x+π/4)cos(x-π/4)=√3sin2x+2sin(x+π/4-π/2)cos(x-π/4)=√3sin2x+sin(2x-π/2)=√3sin2x

sinθ+√3cosθ=2cos(θ-φ)=>2sin(θ+π/3)=2cos(θ-φ)=>sin(θ+π/3)=cos(φ-θ)=>(θ+π/3)+(φ-θ)=2kπ+π/2=>φ=2kπ+π/2-

[cos^4(π/3+α)]-[cos(π/6-α)]^2=[cos(π/3+α)]^4-[sin(π/3+α)]^4=[cos(π/3+α)]^2-[sin(π/3+α)]^2=cos(2π/3+2

f(x)=(cosx)^4-(sinX)^4+2√3sinxcosx=[(cosx)^2+(sinx)^2][(cosx)^2-(sinx)^2]+√3sin2x=(cosx)^2-(sinx)^2+

题目还有问题,应该是“cos²α+cos²β+√2cosα×cosβ=1/2”丢了根号2吧?cos²α+cos²β+cosαcosβ=(1+cos2α)/2+(