Giải dùm mình ạ. Thankssss 1. x = 6cos(2πt +π/4) xác định thời gian từ lúc xuất phát đến x=3 cm lần thứ 2 2. x= 6cos (2πt) xác định thời gian vật đi được từ lúc xuất phát qua vị trí cân bằng lần thứ 5

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