# Vector Space of Bounded Sequences

by bugatti79
Tags: bounded, sequences, space, vector
 P: 660 1. The problem statement, all variables and given/known data Consider the vector space l_infty(R) of all bounded sequences. Decide whether or not the following norms are defined on l_infty(R) . If they are, verify by axioms. If not, provide counter example. 2. Relevant equations x in l_infty(R); x=(x_n), (i) || ||_# defined by ||x||_#=|x_1|, (ii) |\ ||_infty defined by || ||_infty =sup |x_n| for n in N 3. The attempt at a solution (i) a) Since x is in l_infty(R), there exist k_x >0 s.t |x_n| <=k_x for all n in N y is in l_infty(R), there exist k_y>0 s.t |y_n| <=k_y for all n in N ||x+y||_#=||(x_n+y_n)||_#=|x_n+y_n|. Now we have that |a+b| <=|a|+|b|, therefore <=|x_n|+|y_n| <=k_x+k_y for all n in N <=||x||_#+||y||_# b) ||ax||_#=|ax_1| =|a| |x_1| =|aA ||x||_# Axioms c) and d) I dont know how to attempt for this space (ii) || ||_infty =sup |x_n| for n in N Let x be in l_infty(R), x=(x_1) a) ||x||_infty>=sup|x_n|>=0 where sup|x_n|>-0 for n in N for all x_n in l_infty(R) b) ||x||=0 iff x=0 c) ||ax||_infty =sup|ax_n| =|a| sup|x_n| for n in N =|a| ||x||_infty d) Now sure how to use the trinagle inequality for this space..?
 P: 660 Any review of this folks?

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