{"id":5133,"date":"2021-09-08T20:38:28","date_gmt":"2021-09-08T15:08:28","guid":{"rendered":"https:\/\/mathemerize.com\/?p=5133"},"modified":"2022-01-16T17:03:18","modified_gmt":"2022-01-16T11:33:18","slug":"logarithmic-differentiation","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/logarithmic-differentiation\/","title":{"rendered":"Logarithmic Differentiation – Examples and Formula"},"content":{"rendered":"
Here you will learn formula of logarithmic differentiation with examples.<\/p>\n
Let’s begin –<\/p>\n
We have learnt about the derivatives of the functions of the form \\([f(x)]^n\\) , \\(n^{f(x))}\\) and \\(n^n\\) , where f(x) is a function of x and n is a constant. In this section, we will be mainly discussing derivatives of the functions of the form \\([f(x)]^{g(x)}\\) where f(x) and g(x) are functions of x x. To find the derivative of this type of functions we proceed as follows :<\/p>\n
Let y = \\([f(x)]^{g(x)}\\). Taking logarithm of both the sides, we get <\/p>\n
log y = g(x) . log{f(x)}<\/p>\n
Differrentiating with respect to x, we get<\/p>\n
\\(1\\over y\\) \\(dy\\over dx\\) = g(x) \\(\\times\\) \\(1\\over f(x)\\) \\(d\\over dx\\) ((f(x)) + log {f(x)}.\\(d\\over dx\\)(g(x))<\/p>\n
\\(\\therefore\\) \\(dy\\over dx\\) = y{\\({g(x)\\over f(x)}\\).\\(d\\over dx\\)(f(x)) + log{f(x)}.\\(d\\over dx\\) (g(x))}<\/p>\n
Alternatively, we may write<\/p>\n
y = \\([f(x)]^{g(x)}\\) = \\(e^{g(x)log{f(x)}}\\)<\/p>\n
Differentiating with respect to x, we get<\/p>\n
\\(dy\\over dx\\) = \\(e^{g(x)log{f(x)}}\\) { g(x) \\(\\times\\) \\(1\\over f(x)\\) \\(d\\over dx\\) ((f(x)) + log {f(x)}.\\(d\\over dx\\)(g(x)) }<\/p>\n
\\(\\implies\\) \\(dy\\over dx\\) = \\([f(x)]^{g(x)}\\){\\({g(x)\\over f(x)}\\).\\(d\\over dx\\)(f(x)) + log{f(x)}.\\(d\\over dx\\) (g(x))}<\/p>\n
Example<\/span><\/strong> : Differentiate \\(x^x\\) with respect to x.<\/p>\n Solution<\/span><\/strong> : Let y = \\(x^x\\). Then,<\/p>\n Taking log both sides,<\/p>\n log y = x.log x<\/p>\n \\(\\implies\\) y = \\(e^{x.log x}\\)<\/p>\n On differentiating both sides with respect to x, we get<\/p>\n \\(dy\\over dx\\) = \\(e^{x.log x}\\)\\(d\\over dx\\)(xlogx)<\/p>\n \\(\\implies\\) \\(dy\\over dx\\) = \\(x^x{log x \\times {d\\over dx}(x) + x \\times {d\\over dx}(log x)}\\)<\/p>\n = \\(x^x(log x + x\\times {1\\over x})\\)<\/p>\n \\(\\implies\\) \\(dy\\over dx\\) = \\(x^x(1 + logx)\\)<\/p>\n Example<\/span><\/strong> : Differentiate \\(x^{sinx}\\) with respect to x.<\/p>\n Solution<\/span><\/strong> : Let y = \\(x^{sinx}\\). Then,<\/p>\n Taking log both sides,<\/p>\n log y = sin x.log x<\/p>\n \\(\\implies\\) y = \\(e^{sin x.log x}\\)<\/p>\n On differentiating both sides with respect to x, we get<\/p>\n \\(dy\\over dx\\) = \\(e^{sin x.log x}\\)\\(d\\over dx\\)(sin x.log x)<\/p>\n \\(\\implies\\) \\(dy\\over dx\\) = \\(x^{sin x}{log x {d\\over dx}(sin x) + sin x {d\\over dx}(log x)}\\)<\/p>\n \\(\\implies\\) \\(dy\\over dx\\) = \\(x^{sin x}(cos x.log x + {sin x\\over x}\\))<\/p>\n\n\n