Foundation November 2023 Paper 3 Q15
15 A regular polygon is being constructed inside a circle, centre O.
Part of the construction is shown in this diagram.
Not to scale
(a)
(i) Give a reason why OA = OB. [1]
(ii) Write down the mathematical name of triangle OAB. [1]
(b) The regular polygon is completed.
Work out the sum of the interior angles of the regular polygon. [3]
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| (i) [Two equal] radii oe | 1 | Must refer to radius | |
| (ii) Isosceles | 1 | Condone poor spelling | |
| Answer | Marks | Part marks and guidance | |
|---|---|---|---|
| 2880 | 3 | M2 for \(\left(\frac{360}{20} - 2\right) \times 180\) oe or \(\frac{360}{20} \times (80 + 80)\) oe M1 for \(\frac{360}{20}\) soi 18 or 80 or 160 | For M2 accept \(16 \times 180\) or \(18 \times 160\) or \(\left(180 - \frac{360}{18}\right) \times 18\) oe or \((180 - 20) \times \frac{360}{20}\) 80 or 160 not from 20 + 20 + 20 + … 80 or 160 may be seen in correct place on diagram |