If (a + bi)(a - bi) = 25 and a + b = 7 what is ab?
- 12
- 14
- 16
- None of these
Explanation
(a + bi)(a - bi) = a² + b² = 25
a + b = 7
Square both sides of a + b = 7
(a + b)² = 7²
a² + 2ab + b² = 49
Put a² + b² = 25
25 + 2ab = 49
2ab = 49 - 25
2ab = 24
ab = 12
Last verified on 04-05-2026
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