參考摩友解答+理解後的做法
https://www.youtube.com/watch?v=d4JRK_e6Kkw
https://www.shuxuele.com/algebra/amplitude-period-frequency-phase-shift.html
兩個看完就會啦!
https://www.shuxuele.com/algebra/images/amplitude-period-ex0.svg
18.有一個三角函數y=f(x),其週期是 π,如下圖: 問此函數為何? -阿摩線上測驗