{"id":11672,"date":"2022-08-14T01:42:46","date_gmt":"2022-08-13T20:12:46","guid":{"rendered":"https:\/\/mathemerize.com\/?p=11672"},"modified":"2022-08-14T01:42:53","modified_gmt":"2022-08-13T20:12:53","slug":"if-3-cot-a-4-check-whether-1-tan2aover-1-tan2a-cos2a-sin2a-or-not","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/if-3-cot-a-4-check-whether-1-tan2aover-1-tan2a-cos2a-sin2a-or-not\/","title":{"rendered":"If 3 cot A = 4, check whether \\(1 – tan^2A\\over 1 + tan^2A\\) = \\(cos^2A – sin^2A\\) or not."},"content":{"rendered":"
We have,\u00a0 \u00a03 cot A = 4\u00a0 \u00a0 \\(\\implies\\)\u00a0 cot A = \\(4\\over 3\\) = \\(AB\\over BC\\)\u00a0<\/p>\n
Let\u00a0 AB = 4k, then BC = 3k<\/p>\n
By Pythagoras Theorem,<\/p>\n
\\({AC}^2\\) = \\({AB}^2\\) + \\({BC}^2\\)<\/p>\n
\\(\\implies\\)\u00a0 \\({AC}^2\\) = \\(25k^2\\)<\/p>\n
\\(\\implies\\)\u00a0 AC = 5k<\/p>\n
Thus,\u00a0 tan A = \\(BC\\over AB\\) = \\(3k\\over 4k\\) = \\(3\\over 4\\)<\/p>\n
sin A = \\(BC\\over AC\\) = \\(3k\\over 5k\\) = \\(3\\over 5\\)<\/p>\n
cos A = \\(AB\\over AC\\) = \\(4k\\over 5k\\) = \\(4\\over 5\\)<\/p>\n
Now, \\(1 – tan^2A\\over 1 + tan^2A\\) = \\(16 – 9\\over 16 + 9\\) = \\(7\\over 25\\)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0…………(1)<\/p>\n
and\u00a0 \\(cos^2A – sin^2A\\) = \\(7\\over 25\\)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 ………….(2)<\/p>\n
From (1) and (2), we have :<\/p>\n
\\(1 – tan^2A\\over 1 + tan^2A\\) = \\(cos^2A – sin^2A\\)<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":" Solution : We have,\u00a0 \u00a03 cot A = 4\u00a0 \u00a0 \\(\\implies\\)\u00a0 cot A = \\(4\\over 3\\) = \\(AB\\over BC\\)\u00a0 Let\u00a0 AB = 4k, then BC = 3k By Pythagoras Theorem, \\({AC}^2\\) = \\({AB}^2\\) + \\({BC}^2\\) \\(\\implies\\)\u00a0 \\({AC}^2\\) = \\(25k^2\\) \\(\\implies\\)\u00a0 AC = 5k Thus,\u00a0 tan A = \\(BC\\over AB\\) = \\(3k\\over 4k\\) = \\(3\\over 4\\) …<\/p>\n