For part(b),
My solution is,
##(c_1, c_2, c_3, c_4) = (c_1, 5c_1, -c_1, -3c_1)##
They have taken the case that c_1 = -1, which gives their expression for a linear dependent function as they have shown. However, I'm confused that the functions are linearly dependent for any value of ##c_1 \in...