2cos平方X-5sinXcosX 4cos平方=3,X为锐角,求tanX的值

f(x)=cos(2x-派／6)+cos(2x-5派／6)-2cos平方x+1=2cos[(2x-派／6+2x-5派／6)/2]cos[(2x-派／6-2x+5派／6)/2]-(2cos平方x-1)=

(1+2sinxcosx)/(cos^2x-sin^2x)=(cos^2x+sin^2x+2sinxcosx)/(cos^2x-sin^2x)(上下同除以cos^2x)=(1+tan^2x+2tanx

f(x)=cos(2x-π/6)-cos(2x+π/6)+2cos²x=cos2xcos(π/6)+sin2xsin(π/6)-[cos2xcos(π/6)-sin2xsin(π/6)]+2

我刚答过的题:(I)f(x)=3sin^2x+2√3sinxcosx+5cos^2x=sin^2x+2√3sinxcosx+3cos^2x+2(sin^2x+cos^2x)=sin^2x+2√3sin

f(x)=(sin²x+cos²x)+(√3/2)(2sinxcosx)+cos²x=1+(√3/2)sin2x+(1+cos2x)/2=(√3/2)sin2x+(1/2

1+cos²x-sin²x>02cos²x>0cos²x>0即cos²x≠0x≠kπ+π/2,k∈Z定义域为{x∈R|x≠kπ+π/2,k∈Z}再问：

cos平方x+cos平方(x+a)-2cosa*cosx*cos(x+a)=[cos2x+cos2(x+a)]/2+1-2cosa*cosx*cos(x+a)=cos(2x+a)cosa+1-2cos

f(x)=1/2sinx+1/2cosx(二倍角的正弦、余弦公式)=根号2/2（sinxcos45°+cosxsin45°）=根号2/2sin（x+45°）（1）f(a)=根号2/2sin(a+45°

函数y=(sinx+cosx)平方＋2sin平方x=1+2sinxcosx+2sin^2x=sin2x-cos2x+2=√2sin(2x-π/4)+2

y=sinx^2+根3sinxcosx+2cosx^2=-1/2(1-2sinx^2)+1/2根3*2sinxcosx+2cosx^2-1+3/2=-1/2cos2x+二分之根3倍sin2x+cos2

sin(x-360)=sinxcos(x-270)=cos(x+90)=-sinx1=sin^2x+cos^2x1+sin（x-360度）cos（x-270度）-2cos平方x=sin^2x+cos^

2*(sinxcosx-cos平方x)+1=2sinxcosx-2cos²x+1=2sinxcosx-cos2x=sin2x-cos2x=√2sin(2x-45°)

y=cos²(2x)=cos²2x-1/2+1/2=（cos4x)/2+1/2最小正周期=2π/4=π/2

tanx=2sinx=2/√5,cosx=1/√52sin²x-sinxcosx+cos²x=2*4/5-2/√5*1/√5+1/5=7/5

f(x)=(sinx+cosx)^2-2cos^2x=1--2cos^2x+2sinxcosx=sin2x-cosx=√2sin(2x-π/4)f(x)最小正周期T=πf(-π/12)=-√2sin(

sin(3/2π-2x)=3/5cos(2x)=-3/52cosx^2-1=-3/5cosx=+/-根号5/5tanx=+/-2

cos²(x/2)=(1+cosx)/2所以导数=-(sinx)/2

1-sin(^2)x+2msinx-2m-2

解:⑴f(x)=-1/2+sin(π/6-2x)+cos(2x-π/3)+(cosx)^2=-1/2+sinπ/6cos2x-sin2xcosπ/6+cos2xcosπ/3+sin2xsinπ/3+(