ngoann4 ngoann4
  • 30-03-2015
  • Mathematics
Answered

Verify as an identity: cos(90°+x) = -sinx
I'm not sure how to go about this question



Answer :

crisforp
crisforp crisforp
  • 30-03-2015
cos( a + b ) = cosa×cosb - sina×sinb ; 
a = 90 and b = x ;
But, cos90 = 0 and sin90 = 1;
cos( 90 + x ) = 0 × cosx - 1 × sinx = - sinx ; 
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