{"id":1092,"date":"2017-10-12T01:46:55","date_gmt":"2017-10-12T05:46:55","guid":{"rendered":"http:\/\/blog.richmond.edu\/math320\/?p=1092"},"modified":"2017-10-15T01:12:49","modified_gmt":"2017-10-15T05:12:49","slug":"definitions-10102017","status":"publish","type":"post","link":"https:\/\/blog.richmond.edu\/math320\/2017\/10\/12\/definitions-10102017\/","title":{"rendered":"Definitions 10\/10\/2017"},"content":{"rendered":"<p>Definition of Domain : Given the function <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f+%3A+A+%5Crightarrow+B&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f : A &#92;rightarrow B\" class=\"latex\" \/> we say that the domain of f is the set <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"A\" class=\"latex\" \/>.<\/p>\n<p>As we discussed today in class the domain is not simply all the values that your function can take in but rather all the values that you decide your function will take in.<\/p>\n<p>Definition <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cinfty+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;infty \" class=\"latex\" \/> is the limit- <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim_%7Bx+%5Crightarrow%7D+f%28x%29+%3D+%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim_{x &#92;rightarrow} f(x) = &#92;infty\" class=\"latex\" \/> means that for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=M+%3E+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"M &gt; 0\" class=\"latex\" \/> we can find a <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdelta+%3E0+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;delta &gt;0 \" class=\"latex\" \/> such that whenever <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=0%3C+%5Cmid+x-c+%5Cmid+%3C+%5Cdelta+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"0&lt; &#92;mid x-c &#92;mid &lt; &#92;delta \" class=\"latex\" \/>, it follows that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f%28x%29+%3E+M&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f(x) &gt; M\" class=\"latex\" \/>.<\/p>\n<p>An important part of the definition to note is the part that states for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=M+%3E+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"M &gt; 0\" class=\"latex\" \/> we can find a <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdelta+%3E0+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;delta &gt;0 \" class=\"latex\" \/>. This line implies that there is a different value of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdelta&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;delta\" class=\"latex\" \/> for each value of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=M&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"M\" class=\"latex\" \/> which is why in class today we had to find <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdelta&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;delta\" class=\"latex\" \/> in terms of <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=M&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"M\" class=\"latex\" \/> in order to complete this proof.<\/p>\n<p>Definition 4.2.1 &#8211; Let\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f+%3A+A+%5Crightarrow+B&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f : A &#92;rightarrow B\" class=\"latex\" \/>, and let <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\" \/> be a limit point of the domain <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"A\" class=\"latex\" \/>. We say that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim_%7Bx+%5Crightarrow%7Df%28x%29+%3D+L&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim_{x &#92;rightarrow}f(x) = L\" class=\"latex\" \/> provided that, for all <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;epsilon\" class=\"latex\" \/>, there exists a <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cdelta+%3E+0&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;delta &gt; 0\" class=\"latex\" \/> such that whenever <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=0%3C+%5Cmid+x-c+%5Cmid+%3C+%5Cdelta&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"0&lt; &#92;mid x-c &#92;mid &lt; &#92;delta\" class=\"latex\" \/> (and <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x+%5Cin+A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x &#92;in A\" class=\"latex\" \/>) it follows that $\\mid f(x) -L \\mid &lt; \\epsilon$.<\/p>\n<p>It is interesting to note the difference between the standard definition for functional limits and the definition for <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;infty\" class=\"latex\" \/> as the limit. This difference is due to the fact that mathematical operations are still not well defined when using <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;infty\" class=\"latex\" \/>. The last part of the standard definition of functional limits uses the expression <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cmid+f%28x%29+-L+%5Cmid+%3C+%5Cepsilon&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;mid f(x) -L &#92;mid &lt; &#92;epsilon\" class=\"latex\" \/>. We would not want to use this expression where <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=L+%3D+%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"L = &#92;infty\" class=\"latex\" \/> if we are attempting to rigidly prove that a limit equals <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%5Cinfty&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"&#92;infty\" class=\"latex\" \/> when we cannot even properly define <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f%28x%29+-+%5Cinfty+&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f(x) - &#92;infty \" class=\"latex\" \/>.<\/p>\n<p>Theorem 4.2.3-\u00a0Given <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f%3A+A+%5Crightarrow+%5Cmathbb%7BR%7D&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f: A &#92;rightarrow &#92;mathbb{R}\" class=\"latex\" \/> and limit point <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=c+%5Cin+A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"c &#92;in A\" class=\"latex\" \/>, the following statements are equivalent.<\/p>\n<p>i) <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim_%7Bx+%5Crightarrow+c%7D+f%28x%29+%3D+L&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim_{x &#92;rightarrow c} f(x) = L\" class=\"latex\" \/><\/p>\n<p>ii) For all sequences <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=%28x_n%29+%5Csubseteq+A&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"(x_n) &#92;subseteq A\" class=\"latex\" \/> such that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x_n+%5Cneq+c&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x_n &#92;neq c\" class=\"latex\" \/>, it follows that <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f%28x_n%29+%5Crightarrow+L&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f(x_n) &#92;rightarrow L\" class=\"latex\" \/>.<\/p>\n<p>Since i and ii are equivalent this theorem is used to to define the divergence criterion for functional limits. Mainly the divergence criterion utilizes ii. It says that if two sequences <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x_n\" class=\"latex\" \/> and <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=y_n&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"y_n\" class=\"latex\" \/>\u00a0exist for a function <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=f&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"f\" class=\"latex\" \/> such that\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=x_n+%5Cneq+c&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"x_n &#92;neq c\" class=\"latex\" \/> (and c is a limit point),\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=y_n+%5Cneq+c&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"y_n &#92;neq c\" class=\"latex\" \/> and\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim+x_n+%3D+lim+y_n+%3D+c&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim x_n = lim y_n = c\" class=\"latex\" \/> but if <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim+f%28x_n%29+%5Cneq+lim+f%28y_n%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim f(x_n) &#92;neq lim f(y_n)\" class=\"latex\" \/> we can say\u00a0<img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim_%7Bx+%5Crightarrow%7D+f%28x%29&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim_{x &#92;rightarrow} f(x)\" class=\"latex\" \/> does not exist. Here we see the usefulness of Theorem 4.2.3 because it allows us to split <img decoding=\"async\" src=\"https:\/\/s0.wp.com\/latex.php?latex=lim_%7Bx+%5Crightarrow+c%7D+f%28x%29+%3D+L&#038;bg=ffffff&#038;fg=000&#038;s=0&#038;c=20201002\" alt=\"lim_{x &#92;rightarrow c} f(x) = L\" class=\"latex\" \/> into two requirements that we can then use to define divergence for functional limits.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Definition of Domain : Given the function we say that the domain of f is the set . As we discussed today in class the domain is not simply all the values that your function can take in but rather all the values that you decide your function will take in. Definition is the limit- [&hellip;]<\/p>\n","protected":false},"author":3524,"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":[58823],"tags":[],"class_list":["post-1092","post","type-post","status-publish","format-standard","hentry","category-definitions"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p7L4E1-hC","jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1092","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\/3524"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/comments?post=1092"}],"version-history":[{"count":0,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/posts\/1092\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/media?parent=1092"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/categories?post=1092"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.richmond.edu\/math320\/wp-json\/wp\/v2\/tags?post=1092"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}