# Second order Taylor approximation

Hello,
Can someone explain this to me? In the above case ct=yt-gt
I tried to solve it as a three variable taylor approximation but got a few extra terms that weren't included in the above. So I am a little confused now.
I only need to understand how the first line was derived because I get additional terms with (gt-g)(chit-chi)..https://fbcdn-sphotos-c-a.akamaihd.net/hphotos-ak-xap1/v/t35.0-12/13570139_10210195219259688_119153535_o.png?oh=5a83810acd11160ed4bf6a19de37d6ec&oe=57781CBB&__gda__=1467485097_6da652cc9db77ba174ecad977bc59004

Ssnow
Gold Member
In fact in the Taylor expansion you have also the terms ##u_{G}(G_{t}-G)## and ##u_{\zeta}(\zeta_{t}-\zeta)## but in the formula doesn't appear, I think there are some assumptions that permit to put zero these terms ...

PS. ##\zeta## is not chi that is ##\chi##

Simon Bridge
Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

chiro