1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=

来源:学生作业帮助网 编辑:六六作业网 时间:2024/11/22 23:43:18
1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(c

1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=
1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=

1]已知tana*tanb=2,(*是×)则cos(a+b)*cos(a-b)/(cosa)^2*(cosb)^2=
所需公式:cos(α+β)=cosαcosβ-sinαsinβ
cos(α-β)=cosαcosβ+sinαsinβ
原式=[(cosa*cosb-sina*sinb)*(cosa*cosb+sina*sinb)]/[cos^2a*cos^2b]
=[cos^2a*cos^2b-sin^2a*sin^2b]/[cos^2a*cos^2b] (由上式化简得)
=1-tan^2a*cot^2b
=1-2^2
=-3