ARCH(1) model

why the regression equation is about squared residual while we can use it to forecast variance of residual? not intuitive to me.

Thanks for your help.

same thing.

σ² = E(X – µ)² = E(X²) – µ².

so basically we assume u=0 for rediduals, so that var(residual)=residual^2.

Yup.