- 18 The diagram shows triangle PQR.
Diagram NOT
accurately drawn
P
17.8 cm
360
R
26.3 cm
Calculate the length of PR.
Give your answer correct to 3 significant figures.

The length of PR is 15.8 cm

Step-by-step explanation:

We will solve the question using the cosine rule

In ΔPQR

∵ (PR)² = (PQ)² + (RQ)² - 2(PQ)(RQ)(cos∠Q)

∵ PQ = 17.8 cm

∵ RQ = 26.3 cm

∵ m∠Q = 36°

→ Substitute them in the rule above

∵ (PR)² = (17.8)² + (26.3)² - 2(17.8)(26.3)(cos36)

∴ (PR)² = 316.84 + 691.69 - 936.28(cos36)

∴ (PR)² = 251.0635685

→ Take √ for both sides

∴ PR = 15.8449856

→ Correct it to 3 significant figures

∴ PR = 15.8 cm

∴ The length of PR is 15.8 cm

step-by-step explanation: