Hello everybody

I have to show that this set of vectors a = (e^{-t}, e^{-it}, e^{t}, e^{it }) islinearly independent.

My attempt :

f(x) = k1 * e^{-t}+ k2 * e^{-it}+ k3 * e^{t }+ k4 * ei^{t }f '(x) = k1 * -e^{-t + }k2 * -ie^{-it}+ k3 * e^{t }+ k4 * ie^{i}^{t}

f ''(x) = k1 * e^{-t + }k2 * -e^{-it}+ k3 * e^{t }+ k4 * -e^{i}^{t}

f(0) = k1 * 1 + k2 * 1 + k3 * 1+ k4 * 1 = 0

^{ f '(0) = k1 * -1 + k2 * -i + k3 * 1+ k4 * i = 0 f ''(0) = k1 * 1 + k2 * -1 + k3 * 1+ k4 * -1 = 0 But when I plot this in maple and reduce it I get this : They're linearly dependent but this can't be correct. So I guess I'm doing something wrong but what ? }I would really appreciate it if someone could help me.