{"id":838,"date":"2017-09-19T23:05:36","date_gmt":"2017-09-20T03:05:36","guid":{"rendered":"http:\/\/blog.richmond.edu\/math320\/?p=838"},"modified":"2017-09-19T23:05:36","modified_gmt":"2017-09-20T03:05:36","slug":"muddiest-point-9192017","status":"publish","type":"post","link":"https:\/\/blog.richmond.edu\/math320\/2017\/09\/19\/muddiest-point-9192017\/","title":{"rendered":"Muddiest Point 9\/19\/2017"},"content":{"rendered":"<p>Chapter 2 introduces sequences, series, and several theorems for proving the convergence or divergence for each. However, the theorems cannot be used interchangeably for sequences and series. This Muddiest Point post will distinguish between some theorems for sequences and series.<\/p>\n<p><strong>Convergence Theorems for Sequences<\/strong><\/p>\n<ul>\n<li>The Monotone Convergence Theorem: If a sequence is monotone and bounded, then it converges.<\/li>\n<li>Theorem 2.5.2: Subsequences of a convergent sequence converge to the same limit as the original sequence.<\/li>\n<li>Bolzano-Weierstrass Theorem: Every bounded sequence contains a convergent subsequence.<\/li>\n<li>Cauchy Criterion: A sequence converges if and only if it is a Cauchy Sequence.<\/li>\n<li>We showed in challenge 4 of homework 1 that if <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28b_n%29%5Crightarrow+b&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(b_n)&#92;rightarrow b\" class=\"latex\" \/>, then <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%7Cb_n%7C%5Crightarrow+%7Cb%7C&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"|b_n|&#92;rightarrow |b|\" class=\"latex\" \/>.<\/li>\n<\/ul>\n<p><strong>Convergence Theorems for Series<\/strong><\/p>\n<ul>\n<li>The Cauchy Condensation Test: Suppose <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=b_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"b_n\" class=\"latex\" \/> is decreasing and satisfies <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=b_n+%5Cgeq+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"b_n &#92;geq 0\" class=\"latex\" \/> for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n%5Cin+N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n&#92;in N\" class=\"latex\" \/>. Then the series <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bn%3D1%7D+%5E%5Cinfty+b_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{n=1} ^&#92;infty b_n\" class=\"latex\" \/> converges if and only if the series\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bn%3D1%7D+%5E%5Cinfty+2%5En+b_%7B2%5En%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{n=1} ^&#92;infty 2^n b_{2^n}\" class=\"latex\" \/> converges.<\/li>\n<li>The Cauchy Criterion for Series: The series\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/> converges if and only if, given <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cepsilon+%3E0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;epsilon &gt;0\" class=\"latex\" \/>, there exists an <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=N%5Cin+%5Cmathbb%7BN%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"N&#92;in &#92;mathbb{N}\" class=\"latex\" \/> such that whenever <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n%3Em%5Cgeq+N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n&gt;m&#92;geq N\" class=\"latex\" \/> it follows that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%7Ca_%7Bm%2B1%7D%2B%C2%A0a_%7Bm%2B2%7D%2B...%2Ba_n%7C%3C%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"|a_{m+1}+\u00a0a_{m+2}+...+a_n|&lt;&#92;epsilon\" class=\"latex\" \/>.<\/li>\n<li>Theorem 2.7.3: If the series<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/>\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/> converges, then <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28a_k%29%5Crightarrow+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(a_k)&#92;rightarrow 0\" class=\"latex\" \/>.<\/li>\n<li>Comparison Test: Assume <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28a_k%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(a_k)\" class=\"latex\" \/> and <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28b_k%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(b_k)\" class=\"latex\" \/> are sequences satisfying <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=0%5Cleq+a_k%5Cleq+b_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"0&#92;leq a_k&#92;leq b_k\" class=\"latex\" \/> for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=k%5Cin+%5Cmathbb%7BN%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"k&#92;in &#92;mathbb{N}\" class=\"latex\" \/> i) If\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+b_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty b_k\" class=\"latex\" \/> converges, then\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/> converges. ii) If\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/> diverges, then\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+B_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty B_k\" class=\"latex\" \/> diverges.<\/li>\n<li>Absolute Convergence Test: If the series\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bn%3D1%7D+%5E%5Cinfty+%7Ca_n%7C&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{n=1} ^&#92;infty |a_n|\" class=\"latex\" \/> converges, then\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bn%3D1%7D+%5E%5Cinfty+a_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{n=1} ^&#92;infty a_n\" class=\"latex\" \/> converges as well.<\/li>\n<li>Alternating Series Test: Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28a_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(a_n)\" class=\"latex\" \/> be a sequence satisfying (i) <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=a_1%5Cgeq+a_2%5Cgeq+a_3%5Cgeq...%5Cgeq+a_n%5Cgeq+a_%7Bn%2B1%7D%5Cgeq+...&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"a_1&#92;geq a_2&#92;geq a_3&#92;geq...&#92;geq a_n&#92;geq a_{n+1}&#92;geq ...\" class=\"latex\" \/> and (ii)<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28a_n%29%5Crightarrow+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(a_n)&#92;rightarrow 0\" class=\"latex\" \/>. Then the alternating series\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bn%3D1%7D+%5E%5Cinfty+%28-1%29%5E%7Bn%2B1%7D+a_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{n=1} ^&#92;infty (-1)^{n+1} a_n\" class=\"latex\" \/> converges.<\/li>\n<\/ul>\n<p>Note that while these theorems apply specifically to sequences or series, the convergence of the <strong>series\u00a0<\/strong><img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5CSigma+_%7Bk%3D1%7D+%5E%5Cinfty+a_k&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;Sigma _{k=1} ^&#92;infty a_k\" class=\"latex\" \/> is defined in terms of the <strong>sequence<\/strong> of partial sums <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28s_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(s_n)\" class=\"latex\" \/>. Thus, you can also show the convergence of a series by identifying a formula and showing convergence for its sequence of partial sums.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Chapter 2 introduces sequences, series, and several theorems for proving the convergence or divergence for each. However, the theorems cannot be used interchangeably for sequences and series. This Muddiest Point post will distinguish between some theorems for sequences and series. Convergence Theorems for Sequences The Monotone Convergence Theorem: If a sequence is monotone and bounded, [&hellip;]<\/p>\n","protected":false},"author":3528,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[58822],"tags":[],"class_list":["post-838","post","type-post","status-publish","format-standard","hentry","category-muddiest-point"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p7L4E1-dw","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/838","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/users\/3528"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/comments?post=838"}],"version-history":[{"count":0,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/838\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/media?parent=838"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/categories?post=838"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/tags?post=838"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}