{"id":9258,"date":"2022-01-05T00:16:00","date_gmt":"2022-01-04T18:46:00","guid":{"rendered":"https:\/\/mathemerize.com\/?p=9258"},"modified":"2022-01-05T00:22:13","modified_gmt":"2022-01-04T18:52:13","slug":"prove-that-sin-a-b-sin-a-b-sin2-a-sin2-b","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/prove-that-sin-a-b-sin-a-b-sin2-a-sin2-b\/","title":{"rendered":"Prove that sin (A + B) sin (A – B) = \\(sin^2 A\\) – \\(sin^2 B\\)."},"content":{"rendered":"
We have,<\/p>\n
sin (A + B) sin (A – B) = (sin A cos B + cos A sin B) (sin A cos B – cos A sin B)<\/p>\n
= \\(sin^2 A cos^2 B\\) – \\(cos^2 A sin^2 B\\)<\/p>\n
= \\(sin^2 A (1 – sin^2 B)\\) – \\((1 – sin^2 A) sin^2 B\\)<\/p>\n
= \\(sin^2 A\\) – \\(sin^2 A sin^2 B\\) – \\(sin^2 B\\) + \\(sin^2 A sin^2 B\\)<\/p>\n
= \\(sin^2 A – sin^2 B\\)<\/p>\n
Now, we can also write it as,<\/p>\n
= \\((1 – cos^2 A)\\) – \\((1 – cos^2 B)\\) = \\(cos^2 B\\) – \\(cos^2 A\\)<\/p>\n
Hence, sin (A + B) sin (A – B) = \\(sin^2 A\\) – \\(sin^2 B\\) = \\(cos^2 B\\) – \\(cos^2 A\\)<\/p>\n","protected":false},"excerpt":{"rendered":"
Solution : We have, sin (A + B) sin (A – B) = (sin A cos B + cos A sin B) (sin A cos B – cos A sin B) = \\(sin^2 A cos^2 B\\) – \\(cos^2 A sin^2 B\\) = \\(sin^2 A (1 – sin^2 B)\\) – \\((1 – sin^2 A) sin^2 B\\) …<\/p>\n