Hi,

HUGE gratitude to anyone that can help me on the following "problem". I have tried looking it up in algebraic geometry text books though they are either too advanced or contextulised in a different manner. I don't think it is particularly hard, in fact I am sure it is standard text book stuff, though while I don't understand it properly, it limits my progress on the topic.

Anway,the "problem" can be broken down into a number of steps:

1) My lecture notes first consider an affine algebraic variety V in an n-dimensional affine space over a field K and a point p belonging to it. They say a line L given in parametric form {p + tv: t belongs to K, v a non zero vector} isto V iff for every f belonging to I(V), f(p + tv) has a zero of atleast multiplicty 2 at t = 0 or is identically 0.tangent

What is the motivation for this definition?

2)The tangent space TpV is then defined to be the union of the lines tangent to V at p. The following proposition is then given:

Let f|1,...,f|r be a set of generators for I(V) (where by f|i I mean f sub index i). L is tangent to V at p iff for each j, f|j(p +tv) has a zero of atleast multiplicty 2 at t = 0 or is identically 0.

What is the proof for this?

3) As a corollary to this TpV is an affine subspace of dimension n - rankJp where J is the Jacobian matrix (df|j/dx|i) and Jp is J evaluated at p.

Again what is the proof for this?

Thanks for any help. Rereading this I realise it is a lot to ask, though I've exhausted all other avenues