{"id":9223,"date":"2022-01-03T17:51:22","date_gmt":"2022-01-03T12:21:22","guid":{"rendered":"https:\/\/mathemerize.com\/?p=9223"},"modified":"2022-01-03T19:13:31","modified_gmt":"2022-01-03T13:43:31","slug":"what-is-the-formula-of-cosa-b-2","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/what-is-the-formula-of-cosa-b-2\/","title":{"rendered":"What is the Formula of Cos(A – B) ?"},"content":{"rendered":"
In this post you will learn what is the formula for cos (A – B) with examples.<\/p>\n
The formula of cos(A – B)<\/strong> is cos A cos B + sin A sin B<\/strong>.<\/p><\/blockquote>\n
Example<\/span><\/strong> : If sin A = \\(3\\over 5\\) and cos B = \\(9\\over 41\\), find the value of cos (A – B).<\/p>\n
Solution<\/span><\/strong> : We have,<\/p>\n
sin A = \\(3\\over 5\\) and cos B = \\(9\\over 41\\)<\/p>\n
\\(\\therefore\\) cos A = \\(\\sqrt{1 – sin^2 A}\\) and sin B = \\(\\sqrt{1 – cos^2 B}\\)<\/p>\n
\\(\\implies\\) cos A = \\(\\sqrt{1 – {9\\over 25}}\\) = \\(4\\over 5\\) and sin B = \\(\\sqrt{1 – {81\\over 1681}}\\) = \\(40\\over 41\\)<\/p>\n
Now, By using above formula,<\/p>\n
cos (A – B) = cos A cos B – sin A sin B<\/p>\n
= \\(4\\over 5\\) \\(\\times\\) \\(9\\over 41\\) + \\(3\\over 5\\) \\(\\times\\) \\(40\\over 41\\) = \\(156\\over 205\\)<\/p>\n
Example<\/span><\/strong> : Find the value of cos 15.<\/p>\n
Solution<\/span><\/strong> : cos 15 = sin (45 – 30)<\/p>\n
By using above formula,<\/p>\n
cos (45 – 30) = cos 45 cos 30 – sin 45 sin 30<\/p>\n
\\(\\implies\\) cos 15 = \\(1\\over \\sqrt{2}\\) \\(\\times\\) \\(\\sqrt{3}\\over 2\\) + \\(1\\over \\sqrt{2}\\) \\(\\times\\) \\(1\\over 2\\)<\/p>\n
\\(\\implies\\) cos 15 = \\(\\sqrt{3} + 1\\over 2\\sqrt{2}\\)<\/p>\n","protected":false},"excerpt":{"rendered":"
In this post you will learn what is the formula for cos (A – B) with examples. Cos (A – B) Formula : The formula of cos(A – B) is cos A cos B + sin A sin B. Example : If sin A = \\(3\\over 5\\) and cos B = \\(9\\over 41\\), find the …<\/p>\n