sinとcosは表裏一体
①https://stand.fm/episodes/5f83d91c93ba4367cdcf6998
②https://stand.fm/episodes/5f83dc918f5bc05ac03a902a
③https://stand.fm/episodes/5f85867293ba43ed08cf83e8
⑤https://stand.fm/episodes/5f90f0e8bfd83156f137aec3