Algebraic multiplicity is the number of times of occurance of an eigenvalue and geometric multiplicity is the number of linearly independent eigenvectors associated with that eigenvalue.
@Issam vectorspece V is generated by a nonzero vector v1. So its of dimension 1. Is it not clear? Then for the next, we know that Rn is of dimension n and so Rn has an orthogonl basis. So the space spanned by the n-1 orthogonalvectors to v1 is W and is o dmension n-1.Is this not clear?
If the the multiplicity of λ1 > 1, then you find v2 in W,
you assumed it belongs to the eigenspace of the eigenvalue λ1 .Why?
If the the multiplicity of λ1 > 1, then the restriction of A to W is a linear operator from W to W. So it has λ1 as an eigenvalue nd the eigenvector then definitely belong to W and where else?
(In m1 steps we get m1 linearly independent eigenvectors associated with λ1 and nothing more further.) is not clear.
In m1 steps the occurence of λ1 as an eigenvalue to the restricted operator A ends. and by very construction the m1 eigevectors associated with λ1 are lin independent too.