for example, there is a function f(x)= x3+ax2+bx+c=0 with roots Q,W,E
then teachers told me that by substituting y=x2 , then we can find out f(y)=0 s.t. it has roots Q2,W2,E2
but why such substition can help us to find out equations with root Q2,W2,E2? What are the reasons behind?
Thanks for your kind helpings