NECO 2022 · Paper 1 · Q36

Sine & cosine rules
Angles, triangles & polygons

In an isosceles triangle $MNO$ , where $\overline{MN} = \overline{MO} = 6$ cm and $\angle NMO = 112^\circ$ , calculate $\overline{NO}$ , correct to 2 significant figures.

Worked solution (try it first)

Use the cosine rule: $NO^2 = 6^2 + 6^2 - 2(6)(6)\cos 112^\circ$ .
$\cos 112^\circ \approx -0.3746$ , so $NO^2 \approx 72 + 26.97 = 98.97$ .
$NO \approx 9.948$ cm, which is 9.9 cm to 2 significant figures, option B.

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