Chapter 12 - Section 12.1 - Curves in Space and Their Tangents - Exercises - Page 650: 34

$u'=\lt 0,0,0 \gt =0$

Consider, $c(t)=\lt c_1, c_2, c_3 \gt$ Here, $c_1, c_2, c_3$ are taken as constants Since, $u=c \implies \dfrac{d}{dt}u=\dfrac{d}{dt}c$ or, $u'=\lt \dfrac{d}{dt}c_1, \dfrac{d}{dt}c_2, \dfrac{d}{dt}c_3 \gt$ Thus $u'=\lt 0,0,0 \gt =0$