1.已知X,Y均为锐角,若cosX=4/5,cos(X+Y)=3/5 ,求sinY的值 2.已知sinM=1/3,M是锐角,求cos(M+60)值

问题描述:

1.已知X,Y均为锐角,若cosX=4/5,cos(X+Y)=3/5 ,求sinY的值 2.已知sinM=1/3,M是锐角,求cos(M+60)值

1 解 ∵X是锐角,∴sinX=3/5 cos(X+Y)=cosXcosY-sinXsinY=4/5cosY-3/5sinY∴4/5cosY-3/5sinY=3/5∴cosY=(3sinY+3)/4又(sinY)^2+(cosy)^2=1代入自己求解吧.2 ∵M是锐角,∴cosM=(2√2)/3cos(M+60)=cosMcos6...额,1/27? 第一个