תשובה:
#v (7) = (16-sqrt2 pi) / 8 #
הסבר:
#v (t) = d / (d t) p (t) #
#v (t) = d / (d t) (2t-cos (pi / 4t)) #
#v (t) = 2 + pi / 4sin (pi / 4t) #
#v (7) = 2 + pi / 4sin (pi / 4 * 7) #
#v (7) = 2 + pi / 4 * (- sqrt2 / 2) #
#v (7) = 2- (sqrt2pi) / 8 #
#v (7) = (16-sqrt2 pi) / 8 #