ok i dont see how the book came up with the substitution of u= y^-1

so here is the problem..

(t^2)dy/dt + y^2 = ty

my question is this, if u = y^(1-n) wouldnt n = 0?

i think the book may have made a mistake on this problem....can someone please check the problem and see if the substitution is correct? thanks in advance..