Welke gelijkheid
is correct ?

(voor alle hoeken α ) 		A.   − sin(90° − α) = sin(α − 90°)
B.   − sin(90° − α) = sin(90°+ α)
C.   − cos(90° − α) = cos(α − 90°)
D.     cos(90° − α) = cos(α + 90°)
E.   − cos(90° − α) = cos(90° − α)
                 

[ 4-2226 - op net sinds 23.6.09-(E)-29.10.2023 ]

Translation in   E N G L I S H

Which equality is correct ?

( for all α ) 		A.   − sin(90° − α) = sin(α− 90°)
B.   − sin(90° − α) = sin(90°+α)
C.   − cos(90° − α) = cos(α− 90°)
D.   − cos(90° − α) = cos(α+ 90°)
E.   − cos(90° − α) = cos(90° − α)

Oplossing - Solution

− sin(90° − x) = − cos x
sin (x − 90°) = − sin(90° − x) = − cos x
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sin (90° + x) = cos (−x) = cos x
− sin (90° − x) = − cos x
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cos(90° − x) = sin x
cos (90° + x) = sin (−x) = − sin x