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CBSE Class 11-science Answered

Prove that : cos(A + B) =cosAcosB - sinAsinB
Asked by sunil2791 | 08 Dec, 2017, 06:32: PM
answered-by-expert Expert Answer
begin mathsize 16px style We space know space that space cos left parenthesis straight A minus straight B right parenthesis equals cos space AcosB plus sinAsinB Now comma space consider space cos left parenthesis straight A plus straight B right parenthesis. Let space straight A equals straight A space and space straight B equals negative straight B Then comma cos left parenthesis straight A plus straight B right parenthesis equals cos left square bracket straight A minus left parenthesis negative straight B right parenthesis right square bracket space space space space space space space space space space space space space space space space space space equals cosAcos left parenthesis negative straight B right parenthesis plus sinAsin left parenthesis negative straight B right parenthesis space space space space space space space space space space space space space space space space space space space equals cos space AcosB minus sinAsinB space space space space space space left square bracket since space cos left parenthesis negative straight B right parenthesis equals cosB space and space sin left parenthesis negative straight B right parenthesis equals negative sinB right square bracket end style
Answered by Rashmi Khot | 09 Dec, 2017, 06:28: PM

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CBSE 11-science - Maths
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