作业帮设a为锐角,若cos(a π 6)=4 5,则
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答案：3√10/10分析：先根据诱导公式进行化简整理,然后求出tanA,最后根据同角三角函数关系求出sinA即可．∵2tan(π-A)-3cos(π/2+B)+5=0,tan（π+A）+6sin（π+
/>a是锐角π/2
α+β=θ+φ=π/2所以有cosβ=sin(π/2-β)=sinα,cosθ=sin(π/2-θ)=sinφa*b=cosα*cosθ+cosβ*cosφ=cosα*sinφ+sinα*cosφ=s
是关于三角函数的化简啊1)a*b=cosa*sin(π/4-a)+sina*cos(π/4-a)=sin（π/4）=根2/22)最小值的求是:|c|*|c|=|a|*|a|+2ab+|b|*|b|=1
a为锐角,cos(a+π/6)=4/5所以,sin(a+π/6)=3/5sin(2a+π/3)=2sin(a+π/6)cos(a+π/6)=2×(3/5)×(4/5)=24/25cos(2a+π/3)
设b=a+π/6,sinb=3/5,sin2b=2sinbcosb=24/25,cos2b=7/25sin（2a+π/12）=sin（2a+π/3-π/4）=sin（2b-π/4）=sin2bcosπ
cos(2a+π/3)=2cos²(a+π/6)-1=7/25a为锐角,则：2a+π/3∈(π/3,π/2)∴sin(2a+π/3)=24/25sin(2a+π/12)=sin[(2a+π/
50分之17倍根号2
a为锐角,cos(a+π/6)=3/5则：sin(a+π/6)=4/5sin(a-π/12)=sin[(a+π/6)-π/4]=sin(a+π/6)cos(π/4)-cos(a+π/6)sin(π/4
sin（2a+π/12）=sin【2(a+π/6)—π/4】=sin2(a+π/6)cos(π/4）—cos2(a+π/6)sin(π/4）因为cos(a+π/6)=4/5,a为锐角,所以0
设A+π/6=α,则2A+π/12=2α-π/4cosα=4/5,α为锐角,sinα=3/5,所以sin2α=2sinαcosα=24/25,cos2α=2(cosα)^2-1=7/25sin(2A+
a为锐角,cos(a+π/6)=3/5则：sin(a+π/6)=4/5sin(a-π/12)=sin[(a+π/6)-π/4]=sin(a+π/6)cos(π/4)-cos(a+π/6)sin(π/4
设α为锐角,若cos(α+π/6)=4/5,求sin（2α+π/12）,cos(α+π/6)=4/5sin(α+π/6)=3/5,sin（2α+π/3）=24/25cos（2α+π/3）=7/25si
a//b,可得：a=tb,所以有：3=√3t解得：t=√3sina=cosat所以：sina/cosa=t即：tana=√3 得：a=60°
本题可以利用角的变换技穷,直接解方程比较麻烦.a是锐角则0
设sina-cosa=t则2sinacosa=1-t^21-t^2+(1/3)t=13t^2-t=0t=0或t=1/3sinacosa=1/2或4/9tana+cota=1/sinacosa=9/4t
a∈(0,90)a+30∈(30,120)sin(a+30)>0sin(a+30)=3/5sin(2a+60)=2sin(a+30)cos(a+30)=24/25又cos(a+30)>cos45,a+