Simplification question for IBPS, SBI, RBI, clerk, PO, UPSC, State-PSC, Railways, SSC

[Q] If a - b = 3 and a² + b² = 29, find the value of ab.
(a) 40
(b) 10
(c) 30
(d) 20

Solution

Answer    (b)
Explanation
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2ab = (a² + b²) - (a - b)²
   = 29 - 9 = 20
   ab = 10.