数学下面的x是被她cosa+cosx=1/2 sina+sinx/=1/3求cos(a~x)
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数学下面的x是被她cosa+cosx=1/2 sina+sinx/=1/3求cos(a~x)
数学下面的x是被她
cosa+cosx=1/2 sina+sinx/=1/3求cos(a~x)
数学下面的x是被她cosa+cosx=1/2 sina+sinx/=1/3求cos(a~x)
cosa+cosβ=1/2得(cosa+cosβ)^2=1/4即cos^2 a+2cosacosβ+cos^2 β=1/4 (1)
sina+sinβ=1/3得(sina+sinβ)^2=1/9即sin^2 a+2sinasinβ+sin^2 β=1/9 (2)
(1)+(2)得
(cos^2 a+2cosacosβ+cos^2 β)+(sin^2 a+2sinasinβ+sin^2 β)=1/4+1/9
即
(cos^2 a+sin^2 a)+2cosacosβ+2sinasinβ+(cos^2 β+sin^2 β)=1/4+1/9
1+2(cosacosβ+sinasinβ)+1=13/36
cosacosβ+sinasinβ=-59/72
cos(a-β)=cosacosβ+sinasinβ=-59/72
cos(α-β)=-59/72
cosa+cosβ=1/2 sina+sinβ=1/3
(cosa+cosβ)^2=cos^2(a)+2cosacosβ+cos^2(β)=1/4
(sina+sinβ)^2=sin^2(a)+2sinasinβ+sin^2(β)=1/9
cosacosβ+sinasinβ=-59/72
cos(a-β)=cosacosβ+sinasinβ=-59/72
我都忘记了,不过记得方法,先将cos(a~x)拆开,然后求出cosacosβ+sinasinβ