Intermediate June 2017 Unit 2 Q12
12. Show that the triangle below is not a right-angled triangle. [5]

Diagram not drawn to scale
| Scheme | Marks | Comments |
|---|---|---|
| 3x − 2 + 2x + 1 + 5x − 9 = 180 | M1 | |
| 10x = 190 | A1 | |
| x = 19 | A1 | F.T. from ax = b. Allow all 3 marks for x = 19. |
| Substituting x = 19 into at least one expression. | M1 | If x ≠ 19 F.T. ‘their derived value of x’. |
| (3x – 2 =) 55(°) (2x + 1 =) 39(°) (5x – 9 =) 86(°) (So not a right-angled triangle) | A1 | F.T. for this A1 if x > 2. Any two of these expressions correctly evaluated with no incorrect evaluation, provided the sum of the two found is > 90. (statement not required) |