回答: #4、pi# 説明: # "コサインの標準形は"# #色(赤)(棒(ul(|色(白)(2/2)色(黒)(y = acos(bx + c)+ d)色(白)(2/2)|))))# # "振幅" = | a |、 "周期" =(2π)/ b# # "位相シフト" = -c / b、 "垂直シフト" = d# # "ここ" a = -4、b = 2、c = d = 0# #rArr "振幅" = | - 4 | = 4、 "周期" =(2π)/ 2 =π#