AM-2582

Addition formulae

A Math · Secondary 4 · Hard · Addition formulae

Let

\theta

be an angle such that

\cos\theta=-\dfrac{3}{5}

and

\theta

is a reflex angle. Find the exact value of

\sin(\theta-60^\circ)

.

$\dfrac{3\sqrt3-4}{10}$
$-\dfrac{3\sqrt3+4}{10}$
$\dfrac{4-3\sqrt3}{10}$
$\dfrac{3\sqrt3+4}{10}$

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