AM-2546

Addition formulae

A Math · Secondary 4 · Medium · Addition formulae

Given that

\cos x = \dfrac{4}{5}

and

0^\circ<x<90^\circ

, find the exact value of

\cos\left(x+\dfrac{\pi}{6}\right)

.

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

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