cosa等于4/3
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1+cos2a/2
(4sinA-2cosA)/(5cosA+3sinA)=(4tanA-2)/(5+3tanA)=(4*3-2)/(5+3*3)=5/7(sinA-cosA)^2=1-2sinAcosA=1-sin2A
sina+cosa=3/4(sina+cosa)^2=9/16,sinacosa=-7/32sina-cosa=√23/4sin^3a-cos^3a=(sina-cosa)(sin^2a+sinaco
始边为x的正轴,把点在坐标中描出来,则有sina=-4/5cosa=3/5tana=-4/3所以sina+cosa+tana=-23/15
tana=2,则cota=1/2sina/cosa=tana=2sina=2cosa因为sin²a+cos²a=1所以cos²a=1/5sin²a=4/5sin
(√3b-c)cosA=acosC(√3sinB-sinC)cosA=sinAcosC√3sinBcosA=sinAcosC+sinCcosA√3sinBcosA=sin(A+C)√3sinBcosA
tana=2=sina/cosa则sina=2cosa故原式=(cosa+3sina)/(cosa-4sina)=(cosa+6cosa)/(cosa-8cosa)=7cosa/(-7cosa)=-1
tanA=3tanA^2=9=sinA^2/cosA^2sinA^2+cosA^2=1sinA^2=9/10cosA^2=1/10sinA^2*cosA^2=9/100sinA*cosA=3/10
tana=sina/cosa=3/4a//b=>sina/3=cosa/4=>sina/cosa=3/4再问:sina=3k,cosa=4k,tana=sina/cosa=3/4再答:嗯,前题是K不等
tanA大于0,说明角A在第一或第三象限,sinA乘以cosA大于零,结果为3/10
sina/cosa=tana=-1/3cosa=-3sina(sina+2cosa)/(5cosa-sina)=(sina-6sina)/(-15sina-sina)=-5sina/(-16sina)
/>sina-cosa/cosa+sina=(tana-1)/(1+tana)分子分母同时除以cosa=[tana-tan(π/4)-tana]/[1+tan(π/4)tana]=tan(a-π/4)
1+cosa=2cos²(a/2)sina=2sin(a/2)cos(a/2)所以(1+cosa)/sina=cot(a/2)
cosA+sinA=√2/2*cosA+√2/2*sinA=√2cos(A-π/4)
sin(2π-a)=4/5sin(-a)=4/5sina=-4/5a∈(3/2π,2π),cosα>0cosα=根号(1-sin^2α)=根号{1-16/25}=3/5(sina+cosa)/(sin
(3cosa-2sina)²=139cos²a-12sinacosa+4sin²a=139cos²a-12sinacosa+4sin²a=13sin&
(4sina+cosa)/(sina+cosa) 分子分母同时除以cosa得=(4tana+1)/(tana+1)=(4×2+1)/(2+1)=9/3=3
tana=2/3(cosa-sina)/(cosa+sina)=(1-tana)/(1+tana)=(1-2/3)/(1+2/3)=(1/3)/(5/3)=1/5请首先关注【我的采纳率】如果不懂,请继