Foundation November 2017 Paper 1 Q18
18 ABCD is a quadrilateral.
Sides are extended as shown.
Not drawn accurately
Show that \(\; x = 100°\) [3 marks]
| Answer | Mark | Comments |
|---|---|---|
| Alternative method 1 | ||
| Angle DAB = 70 | B1 | may be on diagram |
| Angle ABC \(= 360 -\) their \(70 - 90 - 120\) or Angle ABC = 80 | M1 | may be on diagram |
| Valid reason | A1 | eg \(180 - 80 = 100\) \(80 + 100 = 180\) angles on a straight line add to 180 \((360 - 80 - 80)/2 = 100\) |
| Alternative method 2 working backwards from \(x = 100\) | ||
| Angle ABC \(= 180 - 100\) or Angle ABC = 80 | M1 | may be on diagram |
| Angle DAB \(= 360 -\) their \(80 - 90 - 120\) or Angle DAB = 70 | M1dep | may be on diagram |
| Valid reason | A1 | eg opposite angles are equal vertically opposite angles (are equal) \(180 - 70 = 110\) and \(180 - 110 = 70\) |
Additional guidance
Incorrect angles seen anywhere around A or B cannot score the A1