Answer:
- 13 or - 11
Step-by-step explanation:
a + b = 7 . . . (1) and ab = 12 . . . (2)
Make b the subject of the formula,
b = 7 - a, then substitute in (2).
a(7 - a) = 12
7a - a² = 12 Re-arrange
a² - 7a + 12 = 0
By Factorization
a²- 3a - 4a + 12 = 0
a(a - 3) - 4(a - 3) = 0
(a - 3)(a - 4) = 0
a = 3 or a = 4
When a = 3,
b = 7 - 3
b = 4
When a = 4
b = 7 - 4
b = 3
Therefore, when a = 3, b = 4
a – ab – b = 3 - 3×4 - 4
= 3 - 12 - 4
= - 13
when a = 4, b = 3
a – ab – b = 4 - 4 × 3 - 3
= 4 - 12 - 3
= - 11
Therefore,
a – ab – b = - 13 or - 11
