{"id":6104,"date":"2021-10-07T17:32:17","date_gmt":"2021-10-07T12:02:17","guid":{"rendered":"https:\/\/mathemerize.com\/?p=6104"},"modified":"2021-10-08T01:35:16","modified_gmt":"2021-10-07T20:05:16","slug":"direction-cosines-and-direction-ratios-of-line","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/direction-cosines-and-direction-ratios-of-line\/","title":{"rendered":"Direction Cosines and Direction Ratios of Line"},"content":{"rendered":"
In this post you will learn how to find direction cosines and direction ratios of line of the vector with examples.<\/p>\n
Let’s begin –<\/p>\n
\nThe direction cosines of a line are defined as the direction cosines of any vector whose support is the given line.<\/p>\n<\/blockquote>\n
It follows from the above definition if A and B are two points on a given line L, then the direction cosines of vectors \\(\\vec{AB}\\) or, \\(\\vec{BA}\\) are the direction cosines of line L. Thus, if \\(\\alpha\\), \\(\\beta\\), \\(\\gamma\\) are the angles which the line L makes with the positive direction of x-axis, y-axis and z-axis respectively, then its direction cosines are either, \\(cos\\alpha\\), \\(cos\\beta\\), \\(cos\\gamma\\) or – \\(cos\\alpha\\), – \\(cos\\beta\\), – \\(cos\\gamma\\).<\/p>\n
Therefore, if l, m, n are direction cosines of a line, then -l, -m, -n are also its direction cosines and we always have<\/p>\n
\n\\(l^2 + m^2 + n^2\\) = 1<\/p>\n<\/blockquote>\n
If A\\((x_1, y_1, z_1)\\) and B\\((x_2, y_2, z_2)\\) are two points on a line L, then its direction cosines are<\/p>\n
\n\\(x_2 – x_1\\over AB\\), \\(y_2 – y_1\\over AB\\), \\(z_2 – z_1\\over AB\\) or \\(x_1 – x_2\\over AB\\), \\(y_1 – y_2\\over AB\\), \\(z_1 – z_2\\over AB\\)<\/p>\n<\/blockquote>\n
Direction Ratios<\/strong><\/h4>\n
\nThe direction ratios of a line are proportional to the direction ratios of any vector whose support is the given line.<\/p>\n<\/blockquote>\n
If A\\((x_1, y_1, z_1)\\) and B\\((x_2, y_2, z_2)\\) are two points on a line L, then its direction ratios are proportional to<\/p>\n
\n\\(x_2 – x_1\\), \\(y_2 – y_1\\), \\(z_2 – z_1\\)<\/p>\n<\/blockquote>\n
Example<\/strong><\/span> : Find the direction cosines and direction ratios of the line whose end points are A(1, 2, 3) and B(5, 8, 11).<\/p>\n
Solution<\/span><\/strong> : We have, A(1, 2, 3) and B(5, 8, 11)<\/p>\n
Direction ratios<\/strong> = (4, 6, 8)<\/p>\n
AB = \\(\\sqrt{16 + 36 + 64}\\) = \\(\\sqrt{116}\\)<\/p>\n
Direction Cosines<\/strong> = (\\(4\\over \\sqrt{116}\\), \\(6\\over \\sqrt{116}\\), \\(8\\over \\sqrt{116}\\)).<\/p>\n\n\n