Question

If a − b = 5 and ab = 6, find a + b.

Answer 1

Here, a − b = 5, ab = 6,

Thus,

(a + b)² − (5)² = 4 × 6  ...[Using (a + b)² − (a − b)² = 4ab]

(a + b)² − 25 = 24

−24 − 25 = (a + b)²

(a + b)² = −49

a + b = `±sqrt49`

∴ a + b = ±7