Question

If a + b = 9 and ab = 18, find a − b.

Answer 1

Here, a + b = 9, ab = 18

Thus,

(9)² − (a − b)² = 4 × 18  ...[Using (a + b)² − (a − b)² = 4ab]

81 − (a − b)² = 72

(a − b)² = 81 − 72

∴ (a − b)² = 9

∴ a − b = `± sqrt9`

∴ a − b = ± 3