EM-1337

Cosine rule

E Math · Secondary 3 · Medium · Cosine rule

In

\triangle PQR

, side

PQ = 12\text{ cm}

, side

PR = 15\text{ cm}

and angle

QPR = 80^\circ

. Using the cosine rule, find the length of side

QR

.

$17.5\text{ cm}$
$13.0\text{ cm}$
$19.2\text{ cm}$
$21.0\text{ cm}$

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