tan75

化弦，通分 tan75°+tan15° =sin75°/cos75°+sin15°/cos15° =(sin75°cos15°+cos75°sin15°)/(cos75°cos15°)=sin(75°+15°)/(sin15°cos15°)=1/(1/2sin30°)=4

1、若BC是底边，BC中线高 h = (BC/2)tan75° = 2 (tan30° + tan45° )/(1 - tan30°tan45° )= 2 ( √3/3 + 1 )/(1 - √3/3 )= 2√3/3 + 4；三角形面积 S = BC h/2 = 2( 2√3/3 + 4 )= 4√3/3 + 8 平方厘米 ；2、若BC是腰，底边长度 L = 2BC...

(1+tan75°)/(1-tan75°)= (tan45° + tan75°)/(1 - tan45° tan75°)= tan(45° +75°)=tan120° =-tan60° =-根号3 亲,新的1年开始,祝好事接2连3,心情4季如春,生活5颜6色,7彩缤纷,偶尔8点小财,烦恼抛到9霄云外!

原式=4根号2sin(-60°)*cos45°+tan(45°+30°）-tan（45°-30°）=4根号2*（-二分之根号3*二分之根号2）+（tan45+tan30)/(1-tan45*tan30)-(tan45-tan30)/(1+tan45*tan30)=-2根号3+2+根号3-（2-根号3）=0

首先必须知道公式：sin3x=4sinxsin(60+x)sin(60-x)其实很好证明，利用公式sin(x+y)=sinxcosy+sinycosx,y=2x cos3x=4cosxcos(60+x)cos(60-x)这个用cosx=sin(90-x)即可。然后tan3x=(sin3x)/(cos3x)代入得：tan5*tan55*tan65=tan15 所以原式=tg15*tg75=ctg75*tg75=1 ...

化简sin15°-cos15°/sin15°+cos15° sin15°-cos15°/sin15°+cos15° =tan15°-1 / tan15°+1 =tan15°-tan45° / tan15°+1 =tan(15°-45°) =-tan30° =-√3/3 cos^275+cos^275+cos75cos15 cos275°+cos215°+cos75°cos15°的值等于5/4 ...

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3tan105°/(1-tan^2 75°）=3tan(180-75)/(1-(tan75)^2)=-3/2*2tan75/[1-(tan75)^2]=-3/2*tan(75*2)=-3/2*tan(180-30)=-3/2*(-tan30)=3/2*根号3/3 =根号3 /2

（2）tan165°/(1-tan^2 345°)= -tan15°/(1- tan²15°)=(-1/2)*2tan15°/(1- tan²15°)=(-1/2)*tan30° =(-1/2)*(根号3)/3 = - (根号3)/6 .（3）若2tanx+1=0,x属于（0，π）则：tanx=-1/2 解得：x= π - arctan(1/2).（4）函数y=tan(...