AM-2578

Addition formulae

A Math · Secondary 4 · Medium · Addition formulae

Given that

\cos B = \dfrac{3}{5}

and angle

B

is acute, find the exact value of

\cos( B - 45^\circ )

.

$\dfrac{7\sqrt{2}}{10}$
$\dfrac{\sqrt{2}}{10}$
$\dfrac{\sqrt{2}}{5}$
$\dfrac{\sqrt{2}}{2}$

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