EM-1373

Cosine rule

E Math · Secondary 3 · Hard · Cosine rule

In a triangle

ABC

,

AB = 7\text{ cm}

,

AC = 9\text{ cm}

and

BC = 12\text{ cm}

.
Using the Cosine Rule, find

\cos \angle A

.

$-\dfrac{1}{9}$
$\dfrac{1}{9}$
$-\dfrac{7}{9}$
$\dfrac{7}{9}$

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