prove that cos510 cos 330 + sin390 cos120=-1

Asked by science field | 17th Aug, 2014, 05:17: PM

Expert Answer:

cos space 510 space cos space 330 space plus thin space sin space 390 space cos space 120 space equals space minus 1  C o s space 510 space equals space C o s space left parenthesis 360 plus 150 right parenthesis equals C o s space 150 equals C o s left parenthesis 180 minus 30 right parenthesis equals minus C o s space 30 C o s space 330 space equals space C o s space left parenthesis 360 minus 30 right parenthesis equals C o s space 30 S i n space 390 equals space S i n space left parenthesis 360 plus 30 right parenthesis equals S i n space 30 C o s space 120 equals space C o s space left parenthesis 180 minus 60 right parenthesis equals minus C o s space 60  S o space g i v e n space e q u a t i o n space c h a n g e s space t o  minus cos squared 30 minus sin space 30 space cos space 60 equals minus 3 over 4 minus 1 fourth equals minus 1 equals R H S  H e n c e space P r o v e d

Answered by Dharma Teja | 17th Aug, 2014, 11:33: PM