A boy standing cft. behind and opposite the middle of a foothall goal sees that the angle of elevation of the nearer is A and the angle of elevation of the farther one is B. Show that the length of the field is c(tanAcotB-1).
A boy standing cft. behind and opposite the middle of a foothall goal sees that the angle of elevation of the nearer is A and the angle of elevation of the farther one is B. Show that the length of the field is c(tanAcotB-1).
暂无答案
A,B,C are the angles of a triangle, prove that tanA+tanB+tanC=tanAtanBtanC.
Find all the positive angles less than 380° which satisfy the equation sinx+sin2xsin3x = 0.
Find the general term and the sum ofn terms of the series -3,-1,11,39,89,167.
Find the sum of n terms of the series whose nth term is 3(4n+4n²)-5n³.
Find the maximum value of (5+x)(2+x)/(1-x).
Find the maximum value of (7-x)4 (2+x)6 when x lies between 7 and 2.
某人要作一个三角形,要求它的三条高的长度分别是1/13 ,1/11 ,1/5 ,则此人将【 】
记△ABC的内角A,B,C的对边分别为a,b,c,已知b2=ac,点D在边AC上,BDsin∠ABC=asinC.(1)证明:BD=b;(2)若AD=2DC,求cos∠ABC.
在△ABC中,已知B=120°,AC=,AB=2,则BC=【 】
记△ABC的内角A,B,C的对边分别为a,b,c,面积为,B=60°,a2+c2=3ac,则b=______.
在△ABC中,已知a=3,b=2c.(1)若A=2π/3,求S△ABC.(2) 若2sinB-sinC=1,求C△ABC.
在△ABC中,角A,B,C所对的边分别为a,b,c.已知sinA:sinB:sinC=2:1:√2,b=√2.(1)求a的值;(2)求cosC的值;(3)求sin(2C-π/6)的值.
已知a,b,c分别表示△ABC的角A,B,C对边的长,求证:a(sinB-sinC)+b(sinC-sinA)+c(sinA-sinB)=0.
设圆M的方程为(x-3)2+(y-2)2=2,直线l的方程为x+y-3=0,点P的坐标为(2,1),那么【 】
如果实数x,y满足等式(x-2)2+y2=3,那么y/x的最大值是【 】
已知向量=(-1,2),=(3,m),若⊥,则m=________.
已知向量=(1,3),=(3,4),若(-λ)⊥,则λ=________.
已知向量=(2,5),=(λ,4),若//,则λ=_______.
已知a=(2,1),b=(2,-1),c=(0,1),则(a+b)·c=______;a·b=______.
如图,正方形ABCD的边长为3,则∙=__________.
在边长为1的等边三角形ABC中,D为线段BC上的动点,DE⊥AB且交AB于点E,DF//AB交AC于点F,则|2+|的值为__________;(+)∙最小值为__________.