sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b
来源:学生作业帮助网 编辑:作业帮 时间:2024/06/30 01:07:50
![sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b](/uploads/image/z/565442-26-2.jpg?t=sin%26%23178%3B20%C2%B0%2Bsin80%C2%B0sin40%C2%B0%E4%B8%94sin%28a%2Bb%29sin%28a-b%29%3Dsin%5E2a-sin%5E2b)
sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b
sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b
sin²20°+sin80°sin40°且sin(a+b)sin(a-b)=sin^2a-sin^2b
sin²20°+sin80°sin40°
=sin²20°+sin(60°+20°)sin(60°-20°)
=sin²20°+sin²60°-sin²20°
=sin²60°
=3/4