来自冯贺平的问题
已知α,β都是锐角,且cos(α+β)=3/5,sin(α-β)=3/4,求cos2α且α-β?cos(a-b)和sin(a+b)怎么算?
已知α,β都是锐角,且cos(α+β)=3/5,sin(α-β)=3/4,求cos2α
且α-β?
cos(a-b)和sin(a+b)怎么算?
3回答
2020-06-24 16:18
已知α,β都是锐角,且cos(α+β)=3/5,sin(α-β)=3/4,求cos2α且α-β?cos(a-b)和sin(a+b)怎么算?
已知α,β都是锐角,且cos(α+β)=3/5,sin(α-β)=3/4,求cos2α
且α-β?
cos(a-b)和sin(a+b)怎么算?
cos2a=cos[(a+b)+(a-b)]=cos(a+b)cos(a-b)-sin(a+b)sin(a-b)=(3/5)×(√7/4)-(4/5)×(3/4)=(3√7-12)/20
cos(a-b)和sin(a+b)怎么算?
因为cos(a+b)>0且a、b都是锐角,则:0°0,则:0°