Answer
$-2a$
Work Step by Step
RECALL:
(1) $\sin{(-t)} = -\sin{t}$
(2) $\cos{(-t)} = \cos{t}$
(3) $\tan{(-t)} = -\tan{t}$
Use the given and rule (1) above to obtain:
$=-\sin{t} -\sin{t}
\\=-a - a
\\=-2a$
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