{"id":5508,"date":"2021-09-15T17:55:48","date_gmt":"2021-09-15T12:25:48","guid":{"rendered":"https:\/\/mathemerize.com\/?p=5508"},"modified":"2021-11-22T18:11:24","modified_gmt":"2021-11-22T12:41:24","slug":"differentiation-of-log-x","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/differentiation-of-log-x\/","title":{"rendered":"Differentiation of Log x (Logarithmic Function)"},"content":{"rendered":"
Here you will learn differentiation of log x i.e logarithmic function by using first principle and its examples.<\/p>\n
Let’s begin –<\/p>\n
\nThe differentiation of \\(log_e x\\), x > 0 with respect to x is \\(1\\over x\\).<\/p>\n
i.e. \\(d\\over dx\\) \\(log_e x\\) = \\(1\\over x\\)<\/p>\n<\/blockquote>\n
Proof Using first Principle :<\/strong><\/h4>\n
\nLet f(x) = \\(log_e x\\). Then, f(x + h) = \\(log_e (x + h)\\)<\/p>\n
\\(\\therefore\\)\u00a0 \u00a0\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(f(x + h) – f(x)\\over h\\)<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_e (x + h) – log_e x\\over h\\)<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_e (1 + h\/x)\\over h\\)<\/p>\n
Divide and multiply by x in both numerator and denominator,<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_e (1 + h\/x)\\over h\/x\\) \\(1\\over x\\)<\/p>\n
\\(\\implies\\) \\(d\\over dx\\)(f(x)) = \\(1\\over x\\)<\/p>\n
because, [\\(lim_{h\\to 0}\\) \\(log_e (1 + x)\\over x\\) = 1]<\/p>\n
Hence, \\(d\\over dx\\) (\\(log_e x\\)) = \\(1\\over x\\)<\/p>\n<\/blockquote>\n
Example<\/strong><\/span> : What is the differentiation of log 5x ?<\/p>\n
Solution<\/strong><\/span> : Let y\u00a0 = log 5x<\/p>\n
\\(d\\over dx\\) (y) = \\(d\\over dx\\) log 5x<\/p>\n
By using chain rule,<\/p>\n
\\(d\\over dx\\) (y) = \\(1\\over 5x\\) .5 = \\(1\\over x\\)<\/p>\n
Hence, \\(d\\over dx\\) (log 5x) = \\(1\\over x\\)<\/p>\n
(2) Differentiation of \\(log_a x\\) :<\/h3>\n
\nThe differentiation of \\(log_a x\\), a > 0 , a \\(\\ne\\) 1 with respect to x is \\(1\\over x log_e a\\).<\/p>\n
i.e. \\(d\\over dx\\) \\(log_a x\\) = \\(1\\over x log_e a\\)<\/p>\n<\/blockquote>\n
Proof Using first Principle :<\/strong><\/h4>\n
\nLet f(x) = \\(log_a x\\). Then, f(x + h) = \\(log_a (x + h)\\)<\/p>\n
\\(\\therefore\\)\u00a0 \u00a0\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(f(x + h) – f(x)\\over h\\)<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_a (x + h) – log_a x\\over h\\)<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_a (1 + h\/x)\\over h\\)<\/p>\n
By base changing theorem,<\/p>\n
\\(d\\over dx\\)(f(x)) = \\(lim_{h\\to 0}\\) \\(log_e (1 + h\/x)\\over (log_e a)h\\)<\/p>\n
\\(\\implies\\) \\(d\\over dx\\)(f(x)) = \\(1\\over log_e a\\) \\(lim_{h\\to 0}\\) \\(log_e (1 + h\/x)\\over x(h\/x)\\)<\/p>\n
\\(\\implies\\) \\(d\\over dx\\)(f(x)) = \\(1\\over xlog_e a\\)<\/p>\n
because, [\\(lim_{h\\to 0}\\) \\(log_e (1 + h\/x)\\over h\/x\\) = 1]<\/p>\n
Hence, \\(d\\over dx\\) (\\(log_a x\\)) = \\(1\\over xlog_e a\\)<\/p>\n<\/blockquote>\n
Example<\/strong><\/span> : What is the differentiation of \\(log_3 x\\) ?<\/p>\n
Solution<\/strong><\/span> : Let y\u00a0 = \\(log_3 x\\)<\/p>\n
\\(d\\over dx\\) (y) = \\(d\\over dx\\) \\(log_3 x\\)<\/p>\n
By using above formula,<\/p>\n
\\(d\\over dx\\) (y) = \\(1\\over xlog_e 3\\)<\/p>\n
Hence, \\(d\\over dx\\) (\\(log_3 x\\)) = \\(1\\over xlog_e 3\\)<\/p>\n
\nQuestion for Practice<\/h3>\n
What is the Differentiation of log log x ?<\/a><\/p>\n
What is the Differentiation of x log x ?<\/a><\/p>\n
What is the differentiation of log sin x ?<\/a><\/p>\n
What is the differentiation of 1\/log x ?<\/a><\/p>\n
What is the differentiation of \\(log x^2\\) ?<\/a><\/p>\n\n\n