Welke uitdrukking
is de vreemde eend
in de bijt ? 		A.  sin (α − 90°)
B.  sin (90° + α)
C.  cos (180° + α)
D.  cos (α − 180°)
E.  cos (180° − α)
A    B    C    D    E 

[ 4,5-3579 - op net sinds 10.11.02-(E)-30.10.2023 ]

Translation in   E N G L I S H

Four expressions are
equal to each other.

What is the
fifth expression ? 		A.  sin (α − 90°)
B.  sin (90° + α)
C.  cos (180° + α)
D.  cos (α − 180°)
E.  cos (180° − α)

Oplossing - Solution

sin(α − 90°) = − sin(90° − α) = − cos α
sin(90° + α) = cos[ 90° − (90° + α) ] = cos (90° − 90° − α) = cos (− α) = cos α
cos(180° + α) = − cos α   [ α en 180° + α antisupplementair ]
cos(α − 180°) = − cos α   [ α en α − 180° antisupplementair ]
cos(180° − α) = − cos α   [ α en 180° − α supplementair ]
gricha