{"id":1427,"date":"2017-11-13T23:00:24","date_gmt":"2017-11-14T04:00:24","guid":{"rendered":"http:\/\/blog.richmond.edu\/math320\/?p=1427"},"modified":"2017-11-13T23:00:24","modified_gmt":"2017-11-14T04:00:24","slug":"hw-8-challenge-3ab","status":"publish","type":"post","link":"https:\/\/blog.richmond.edu\/math320\/2017\/11\/13\/hw-8-challenge-3ab\/","title":{"rendered":"HW 8: Challenge 3(a,b)"},"content":{"rendered":"<p>Consider the sequence of functions <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g_n%3A%5B0%2C%5Cinfty%5D%5Cto+R&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g_n:[0,&#92;infty]&#92;to R\" class=\"latex\" \/> defined by <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g_n%28x%29%3A%3D%5Cfrac%7Bx%5En%7D%7Bn%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g_n(x):=&#92;frac{x^n}{n}\" class=\"latex\" \/><\/p>\n<p>a) Prove that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28g_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(g_n)\" class=\"latex\" \/> converges uniformly on <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[0,1]\" class=\"latex\" \/> and find <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%3D%5Clim+g_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g=&#92;lim g_n\" class=\"latex\" \/>.<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28g_n%29%3D%28%5Cfrac%7Bx%5En%7D%7Bn%7D%29%3D%5C%7Bx%2C+%5Cfrac%7Bx%5E2%7D%7B2%7D%2C%5Cfrac%7Bx%5E3%7D%7B3%7D%2C%5Chdots%5Cfrac%7Bx%5En%7D%7Bn%7D%5C%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(g_n)=(&#92;frac{x^n}{n})=&#92;{x, &#92;frac{x^2}{2},&#92;frac{x^3}{3},&#92;hdots&#92;frac{x^n}{n}&#92;}\" class=\"latex\" \/><\/p>\n<p>In order to better examine this, look at <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x%3D.5&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x=.5\" class=\"latex\" \/>, then\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28g_n%29%3D%28%5Cfrac%7B.5%5En%7D%7Bn%7D%29%3D%5C%7B.5%2C+%5Cfrac%7B.5%5E2%7D%7B2%7D%2C%5Cfrac%7B.5%5E3%7D%7B3%7D%2C%5Chdots%5Cfrac%7B.5%5En%7D%7Bn%7D%5C%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(g_n)=(&#92;frac{.5^n}{n})=&#92;{.5, &#92;frac{.5^2}{2},&#92;frac{.5^3}{3},&#92;hdots&#92;frac{.5^n}{n}&#92;}\" class=\"latex\" \/>. The limit of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cfrac%7B.5%5En%7D%7Bn%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;frac{.5^n}{n}\" class=\"latex\" \/> as <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n%5Cto%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n&#92;to&#92;infty\" class=\"latex\" \/> is 0. This holds similarly for <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x%5Cin%280%2C1%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x&#92;in(0,1)\" class=\"latex\" \/><\/p>\n<p>For <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x%3D0%2C+0%5En%2Fn%3D0%5C%3B%5Cforall+n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x=0, 0^n\/n=0&#92;;&#92;forall n\" class=\"latex\" \/> and\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x%3D1%2C+1%5En%2Fn%3D1%2Fn%5Cto+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x=1, 1^n\/n=1\/n&#92;to 0\" class=\"latex\" \/>, so <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28g_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(g_n)\" class=\"latex\" \/> converges pointwise to <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%28x%29%3D0%3D%5Clim+g_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g(x)=0=&#92;lim g_n\" class=\"latex\" \/><\/p>\n<p>Let <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\" \/> be arbitrary and choose <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cfrac%7B1%7D%7BN%7D%3C%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;frac{1}{N}&lt;&#92;epsilon\" class=\"latex\" \/> (which exists by Archimedean Property). Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n%5Cgeq+N%2C+x%5Cin%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n&#92;geq N, x&#92;in[0,1]\" class=\"latex\" \/> both be arbitrary.<\/p>\n<p>Examine <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%7Cg_n%28x%29-g%28x%29%7C%3D%7Cg_n%28x%29-0%7C%3D%7C%5Cfrac%7Bx%5En%7D%7Bn%7D%7C&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"|g_n(x)-g(x)|=|g_n(x)-0|=|&#92;frac{x^n}{n}|\" class=\"latex\" \/>. Notice that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%7C%5Cfrac%7Bx%5En%7D%7Bn%7D%7C%5Cleq+%5Cfrac%7B1%7D%7Bn%7D%5Cleq+%5Cfrac%7B1%7D%7BN%7D+%3C%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"|&#92;frac{x^n}{n}|&#92;leq &#92;frac{1}{n}&#92;leq &#92;frac{1}{N} &lt;&#92;epsilon\" class=\"latex\" \/>, since <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n%5Cgeq+N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n&#92;geq N\" class=\"latex\" \/>. Thus, since <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cepsilon%2C+n%2C+%5Ctext%7B+and+%7D+x&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;epsilon, n, &#92;text{ and } x\" class=\"latex\" \/> were arbitrary (within the stated constraints), for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cepsilon%3E0%2C%5Cexists+N%3E%5Cfrac%7B1%7D%7B%5Cepsilon%7D%5Cin+N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;epsilon&gt;0,&#92;exists N&gt;&#92;frac{1}{&#92;epsilon}&#92;in N\" class=\"latex\" \/> such that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g_n%28x%29-g%28x%29%7C%3C%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g_n(x)-g(x)|&lt;&#92;epsilon\" class=\"latex\" \/> whenever <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=n+%5Cgeq+N&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"n &#92;geq N\" class=\"latex\" \/> and <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x%5Cin+%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x&#92;in [0,1]\" class=\"latex\" \/>. Thus by definition of unform converges,\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28g_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(g_n)\" class=\"latex\" \/> converges uniformly on <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[0,1]\" class=\"latex\" \/>.<\/p>\n<p>b) Show that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%3D%5Clim+g_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g=&#92;lim g_n\" class=\"latex\" \/> is differentiable on <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[0,1]\" class=\"latex\" \/> and compute <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%27%28x%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g&#039;(x)\" class=\"latex\" \/>.<\/p>\n<p>As shown in part a)\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%3D%5Clim+g_n%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g=&#92;lim g_n=0\" class=\"latex\" \/>.<\/p>\n<p>Let <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=c%5Cin%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"c&#92;in[0,1]\" class=\"latex\" \/> be arbitrary and consider <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Clim_%7Bx%5Cto+c%7D+%5Cfrac%7Bg%28x%29-g%28c%29%7D%7Bx-c%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;lim_{x&#92;to c} &#92;frac{g(x)-g(c)}{x-c}\" class=\"latex\" \/>. Since <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g\" class=\"latex\" \/> is constant and defined for <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=c&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"c\" class=\"latex\" \/>, this is the same as\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Clim_%7Bx%5Cto+c%7D+%5Cfrac%7B0-0%7D%7Bx-c%7D%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;lim_{x&#92;to c} &#92;frac{0-0}{x-c}=0\" class=\"latex\" \/>. This however, if the definition of the derivative of g at c, which therefore exists. Since <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=c+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"c \" class=\"latex\" \/> was arbitrary, the derivative <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%27%28x%29%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g&#039;(x)=0\" class=\"latex\" \/> exists for all points in <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[0,1]\" class=\"latex\" \/>, and thus by definition of differentiable,<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=g%27%28x%29%3D0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"g&#039;(x)=0\" class=\"latex\" \/> is differentiable on\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5B0%2C1%5D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"[0,1]\" class=\"latex\" \/>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Consider the sequence of functions defined by a) Prove that converges uniformly on and find . In order to better examine this, look at , then\u00a0. The limit of as is 0. This holds similarly for For and\u00a0, so converges pointwise to Let be arbitrary and choose (which exists by Archimedean Property). Let both be [&hellip;]<\/p>\n","protected":false},"author":3527,"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":[58827,58826],"tags":[],"class_list":["post-1427","post","type-post","status-publish","format-standard","hentry","category-challenge-solutions","category-peer-grading"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p7L4E1-n1","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1427","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\/3527"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/comments?post=1427"}],"version-history":[{"count":0,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1427\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/media?parent=1427"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/categories?post=1427"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/tags?post=1427"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}