Mathematics
Senior High
高校2年生の数学II（加法定理）です🙇🏻♀️
解答の2行目で、なぜcos4/5πが2/√2 になるのかが分かりません💦
どなたか教えてください！
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![基本例題の[2]についてです。ここの条件ですが、
a/3<=1<=4a/3とありますが4a... - 1](https://d1e9oo257tadp1.cloudfront.net/uploads/qa_question_image/file/1810404/thumb_l_webp_70236300-B387-4A8D-A246-76C58E626EEE.webp?Expires=1787911772&Signature=Np1zN2-0jhMjeaBbhkns4bfcohn9l1YD2Ss0rrtj71IJEx5ePTILko4nNgQPAHvNI1UspCqFFkQH5V0QvEQ~D4~hRPgMdl-H7m2LxvQV1cdwyiLFLgi8FfIYTPU8dDmdUFBa355~h32nhfPyKQy~rqxClyKmOEBTs-oNaEXdjA6JkTXGbVh-51JR9zoZ9eQXQYkiZPWxRcQU6za0rFK70jECIhryTYWYX~i7a8SUdvtP0fldGW-Xteq9G4N6GLWYLy8qIsEALVIuuNTOITF~JuKBtccHYGSsWVuyEXUlGX5N9T5p5852cG7DgCLmGHs98FkEstTzwS8K7OKv3Sv5XA__&Key-Pair-Id=K2W722D70GJS8W&Expires=1787911772&Signature=fidzZZUlr4SqEN~8Uew1rmdM5QrDuOD0Z-ResfL1fm8K8Sg39Nky-o~0W0zZVolFaEcUs9~hPbZgPiOxsQoHCY5uIQWDK1U6JA6-ncZjUWZ0k~-GtnvJARtBr-EmOwptDBV9Es9BKsL1v9pHYnQbFXm1IotIPm6L28czgbYHwzGmNdVsD9CsHTV0410V-V0beSExkorb4hRsmRF9z-YfGJ9ttxQuM~DbORBLc9xV4NSb55JVCdGY62cFbSUdWI-cHSA2Q0gSxshQsKjhd7sdJDYJmq8Ijlu-XcpICiO1llqST47FlfSYAbXx5bbuohToL8rIOHQePlVDjb5IXA5xOA__&Key-Pair-Id=K2W722D70GJS8W)
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