规定:sin(-x)=-sinx,cos(-x)=cosx,sin(x+y)=sinx·cosy+cosx·siny.据此判断下列等式成立的是_________ (填序号).
①cos(-60°)=—cos60°=![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3389f53711264b0acba3ba6019f8b908.png)
②sin75°=sin(30°+45°)=sin30°·cos45°+cos30°·sin45°=![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2e34f8ef860307d4c133b918472f3200.png)
③sin2x=sin(x+x)=sinx·cosx+cosx·sinx=2sinx·cosx;
④sin(x-y)=sinx·cosy-cosx·siny.
①cos(-60°)=—cos60°=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3389f53711264b0acba3ba6019f8b908.png)
②sin75°=sin(30°+45°)=sin30°·cos45°+cos30°·sin45°=
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2e34f8ef860307d4c133b918472f3200.png)
③sin2x=sin(x+x)=sinx·cosx+cosx·sinx=2sinx·cosx;
④sin(x-y)=sinx·cosy-cosx·siny.
更新时间:2018-01-26 19:59:19
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【知识点】 三角函数综合
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