∫T(t)dt=∫(40+17sin(пt/12))dt (积分上限21,下限9)
=40t + 17∫sin(пt/12)dt(积分上限21,下限9)
=40t +(17*12/п)cos(пt/12) (积分上限21,下限9)
=40(21-9) + (17*12/п)(cos(21п/12)-cos(9п/12))
=480 + (204/п)(cos(7п/4)-cos(3п/4))
=480 - (408/п)cos(3п/4)
=480 - (408/п)cos(3п/4)
=480 + (408/п)sin(п/4)
=480 + (204(根号2)/п)