cosx+cosy

邰菁欣813已知cosx+cosy=1/2,sinx - siny=1/3,求cos(x+y) -
曾养园13487703454 ______[答案] 有cos(x+y)=cosxcosy-sinxsiny又将题目所给式子左右平方,在两个式子左右对应相加为: cos^2x+cos^2y+2cosxcsoy+sin^2x+sin^2y-2sinxsiny=13/36 由cos^2x+sin^2x=1 cos^2y+sin^2y=1 可得 1+2cosxcsoy+1-2sinxsiny=13/36 2cosxcsoy-2sinxsin=59/...

邰菁欣813高一三角函数题cosx+cosy=cosxcosy……cosx+cosy=cosxcosy,cos((x+y)/2)=0.8,则cos((x - y)/2)=?好像要用到什么＂和差化积”与“积化和差”.详细讲一讲, -
曾养园13487703454 ______[答案] 楼上给的公式有问题吧?cosxcosy=1/2*[cos((x+y)/2)+cos((x-y)/2)} 这个有问题.和差化积的公式:sinα+sinβ=2sin[(α+β)/2]cos[(α-β)/2]sinα-sinβ=2cos[(α+β)/2]sin[(α-β)/2]cosα+cosβ=2cos[(α+β)/2]co...

邰菁欣813cos x+cos y=? -
曾养园13487703454 ______ cosx+cosy=2cos[(x+y)/2]cos[(x-y)/2]

邰菁欣813已知x,y∈(0,π),求满足方程cosX+cosy - cos(x+y)=3/2的x,y的值 求过程 -
曾养园13487703454 ______ cosx+cosy=2cos((x+y)/2)*cos((x-y)/2),cos(x+y)=2[cos((x+y)/2)]^2-1 cosX+cosy-cos(x+y)=3/2可以变为2cos((x+y)/2)*cos((x-y)/2)-2[cos((x+y)/2)]^2+1=3/2 整理为4[cos((x+y)/2)]^2-4cos((x+y)/2)*cos((x-y)/2)+1=0① 由△≥0,得16[cos((x-y)/2)]^2-16≥0,即[...

邰菁欣813cosx+cosy=1/2,sinx - siny=1/3,则cos(x+y)=? -
曾养园13487703454 ______[答案] 有cos(x+y)=cosxcosy-sinxsiny又将题目所给式子左右平方,在两个式子左右对应相加为: cos^2x+cos^2y+2cosxcsoy+sin^2x+sin^2y-2sinxsiny=13/36 由cos^2x+sin^2x=1 cos^2y+sin^2y=1 可得 1+2cosxcsoy+1-2sinxsiny...

邰菁欣813已知cosx+cosy=1/2,sinx+siny=1/3,求cos(x - y)的值(要过程,尽量详细点哈,thank you ) -
曾养园13487703454 ______[答案] 由题意可得(cosx+cosy)��=1/4 ①(sinx+siny)��=1/9 ②①+ ②:2cosxcosy+cos��x+cos��y+2sinxsiny+sin��x+sin��y=13/362cosxcosy+2sinxsiny+2=13/36cosxcosy+sinxsiny=-59/72即cos(x-y)=-59/72...

邰菁欣813推一个数学三角函数公式哪位高手帮忙推下面这条公式:cos(x+y)=cosx.cosy - sinx.siny要过程~ -
曾养园13487703454 ______[答案] 在平面直角坐标系xOy中, 设单位向量OA=(cosx,sinx) 单位向量OB=(cosy,siny) 则OA与OB的夹角为x-y 由向量夹角公式得: cos(x-y)=(向量OA·向量OB)/(|OA|*|OB|) =cosxcosy+sinxsiny 将上式中y变为-y 得cos(x+y)=cosxcos(-y)+sinxsin(-y) =cosxcosy-...

邰菁欣813把(cosx+cosy)(cosx - cosy)化为积的形式是什么 -
曾养园13487703454 ______[答案] =cos²x-cos²y =(1+cos2x)/2-(1+cos2y)/2 =(cos2x-cos2y)/2 ={cos[(x+y)+(x-y)]-cos[(x+y)-(x-y)]}/2 =[cos(x+y)cos(x+y)-sin(x+y)sin(x-y)-cos(x+y)cos(x+y)-sin(x+y)sin(x-y)]/2 =-sin(x+y)sin(x-y)

邰菁欣813如果cosx+cosy - cos(x+y)=0,x,y为锐角,求x和y. 要详细过程 -
曾养园13487703454 ______ 由cosx+cosy-cos(x+y)=0,得cosx+cosy=cos(x+y) 即cosx+cosy=cosxcosy-sinxsiny,化简得(1-cosx)(1-cosy)=1+sinxsiny>1,(x,y为锐角) 而1-cosx

邰菁欣813等式cos(x+y)=cosx+cosy在什么情况下成立 -
曾养园13487703454 ______ X=π,Y=π/3; cos(π+π/3)=cosπ+cosπ/3;