设x为锐角,若cos(x 30°)=4 5 ,sin(2x 15°)
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解决方案,cosxcos30°-sinxsin30°+的sinx=0/5√3/2cosx1/2sinx=0/5COS(X-30°)=8/10COS(X-60°)=COS2(X-30°)=2cos^2(
cos(X-cosX)=sin(π/2-X+cosX)带入原式sin(x+sinx)=sin(π/2-x+cosx)x+sinx=π/2-x+cosxsinx-cosx=π/2-2x对于原式左侧有si
α∈(0,π/2)α+π/6∈(π/6,2π/3)cos(α+π/6)=4/5>0∴α+π/6∈(π/6,π/2)∴2α+π/3∈(π/3,π)cos(2α+π/3)=2cos²(α+π/6
sinα=3cosα则tana=3则sinαcosα=sinαcosα/(sin²a+cos²a)=tana/(tan²a+1)=3/(9+1)=3/10
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+
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
设x为锐角,cos(x+π除以6)=五分之四=4/5,∵4/5>√2/2,cos(π除以4)=√2/2∴0
由α为锐角,cosα=35得sinα=45,∴tanα=43-----(3分)又tan(α-β)=13,∴tanβ=tan[α-(α-β)]=tanα−tan(α−β)1+tanαtan(α−β)=4
证明:因为θ是锐角,即0
设x是锐角,sin(360°+x)cos(360°+x)=1/2,sinxcosx=1/2sin^2x+cos^2x=1(sinx+cosx)^2=sin^2x+cos^2x+2sinxcosx=2s
不对30%X-25%X=85或0.3X-0.25X=85
/>(cosα-sinα)/cosα+sinα)=(1-tanα)/(1+tantanα)=(1-3)/(1+3)=-1/2