Hello,

After reading the thread's sticky on how to do DE proofs, I attempted one of my home work questions so could someone let me know if I did it right? I think I did but my confidence in my skills at this stage is low so I feel I need lots of reassurance

Prove lim x^2-4x-12=9

x->-3

in my rough work I basically get it to factor to x^2-4x-21 which is |x-7||x-(-3)|

delta equals epilson/|x-7| and I label |x-7| as M since Delta cannot be defined in terms of x

x is -4<x<-2 if |x-(-3)|<1

M is therefore -2

and Delta becomes E/-2

I won't write out the full proof but basically at the end I say my delta is min {1, E/-2} and that 0<|x-(-3)| <Delta implies that |x^2-4x-21|<Epsilon

Thanks!