设a为锐角,若cos(a加6分之拍)等于4分之5
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/>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
展开后有cosacosβ-sinasinβ=sinacosβ-cosasinβ移项后cosa(sinβ+cosβ)=sina(sinβ+cosβ)a、β是锐角,(sinβ+cosβ)≠0,约掉cosa
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
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
sina+cosa=√5/2两边同时平方,得:1+2sina*cosa=5/4sina*cosa=1/8
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+