If a² + b² = 25 and ab = 12, then    is
 a) 4
 b) 5
 c) 6
 d) 7

KPSC Divisional Accountant-15

7. Solution (a+b)2 = a2 + b2 + 2ab => a+b = 7 (a-b)2 = a2 + b2 - 2ab => a-b = 1