How do you prove cos (90 deg + A) = -sin A?
1 Answer
Feb 25, 2016
see explanation
Explanation:
using
#color(blue)" Addition formula " # • cos(A ± B ) = cosAcosB ∓ sinAsinB (Note sign change )
applying this to the question to obtain:
#cos(90^@ + A ) = cos90^@cosA - sin90^@sinA# you should know the following facts:
#cos90^@ = 0 " and " sin90^@ = 1 #
#rArrcos(90^@ + A ) = 0xxcosA - 1xxsinA = 0-sinA = -sinA#
