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Math·Geometry and Trigonometry·Right triangles and trigonometry

easy

A right triangle has acute angles with measures $a^{\circ }$ and $b^{\circ }$. Which of the following must be true?

A

$\sin a^{\circ }=\cos b^{\circ }$

B

$\sin a^{\circ }=\tan b^{\circ }$

C

$\sin a^{\circ }=\cos (90-b{)}^{\circ }$

D

$\sin a^{\circ }=\sin (90-a{)}^{\circ }$