Bon vite fait, je dirai:
Lambda_s (S^(n-1) inter [-h,h]X[-1,1]^(n-1))<= Lambda_s([-h,h]X[-1,1]^(n-1))
<= lambda_n ([-h,h]X[-1,1]^(n-1)) /lambda_n(B^n)
<= lambda_1([-h,h])*lambda_(n-1) ([-1,1]^(n-1)) /lambda_n(B^n)
<= 2*h*2^(n-1)/lambda_n(B^n)
<=2^n*h/lambda_n(B^n)
si tu as des questions (sur les notations notamment) n'hésite pas!