Question

Prove that :
cos(44°-A) . cos(44+A) + cos(46-A) . cos(46+A) = cos2A​

Answer 1

Answer:

cos^2(44)cos^2A

-sin^2(44)sin^2A+cos^2(46)cos^2A-sin^2(46)s

= cos^2A{cos^2(44)+cos^2(46)}-sin^2A{sin^2(44)+sin^(46)}

=cos^2A{sin^2(46)+cos^2(46)}-sin^2A{cos^2(46)+sin^2(46)}

=cos^2A×1- sin^2A×1

= cos2A